In the general population, about one third suffers from one or more symptoms of insomnia, and about 10% fulfill the criteria for a clinical diagnosis . Insomnia entails substantial individual suffering, and costs to society  through factors such as drug-use, increases in risks for long-term sick-leave, major depression, and hypertension [3–6].
Despite the high prevalence and negative consequences of insomnia, only a small percentage is treated [7, 8], most commonly with pharmacotherapy . However, many individuals with insomnia would prefer non-pharmacological treatment if available [9, 10]. Cognitive behavioral therapy (CBT) has been shown to be effective for insomnia [11–13], and is therefore considered treatment of choice [14, 15]. Still, CBT is provided only to a minority, at least partially due to the limited availability of CBT therapists  and high initial costs .
To improve the availability of effective psychological treatments, self-help protocols have been developed for a number of problems, including anxiety, depression, and tinnitus [e.g. ]. Evaluations have often shown results comparable to face-to-face treatments , while self-help treatments are most likely more cost-effective [20, 21]. Although thorough health-economic studies on the cost-effectiveness of self-help are still in their infancy, the potential for helping more people to a lower cost is obvious. Self-help protocols have been developed also for insomnia, and in a recent meta-analysis, Van Straten & Cuijpers concluded they are effective for individuals with primary insomnia .
However, the majority of patients with insomnia present with a range of co-morbid problems . In earlier studies, these patients were often excluded, since other states such as psychiatric conditions and medical problems including other sleep disorders were considered to cause the insomnia.
This exclusion reduces the generalizability of the empirical support for CBT for insomnia since insomnia only rarely occurs without co-morbid conditions . For example, in one study where insomnia diagnoses were assessed, only 20% of the participants were diagnosed with primary insomnia, while 52% were diagnosed with insomnia secondary to a mental disorder (44%) or to a medical condition or substance abuse (8%) .
The causal direction of the different conditions is often very difficult to establish, possibly due to bi-directional relationships between insomnia and other disorders. Hence, it has been suggested that the term co-morbid (rather than secondary) insomnia be used and that it may not be necessary to treat the "other" disorder first . Indeed, in a recent RCT, Edinger et al  showed that CBT for insomnia delivered individually is useful also for patients with co-morbidities, and a relatively recent review concludes that CBT for insomnia (delivered individually or as group treatments) is promising for individuals with medical and psychiatric co-morbidity . By contrast, data is very limited on self-help treatments for this broader population of insomnia sufferers. It is therefore crucial to find out if the previous positive results shown for individuals with primary insomnia without co-morbidities, also generalize to the larger group of patients including those with co-morbidities.
Therapist guidance can improve the effects of self-help treatments and reduce drop-out rates [21, 28]. This seems true also for self-help CBT for insomnia , although the few studies comparing self-help with and without therapist guidance are limited by rather low power and have excluded individuals with co-morbidities [29, 30]. It is also unclear whether the differences between guided and unguided participants seen directly after treatment are stable over time. In addition, previous evaluations of insomnia treatments have focused mainly on sleep-timing measures, while studies investigating effects of insomnia treatments on daytime functioning and psychological distress are lacking.
The objective of the present study was to compare the effects of a CBT-based self-help treatment for insomnia, given with or without therapist support, to a waiting list control group. To compensate for limitations in previous studies we wanted to study individuals from the general population, including patients with co-morbidities, and to also evaluate day time functioning and psychological distress.
Our hypotheses were that participants would benefit from treatment both directly after the treatment and at three-month follow up, and that support would enhance outcome. We hypothesized that these improvements would be seen in response and remission rates, sleep timing, subjective measures of sleep, and daytime functioning. No differences in outcome due to co-morbid problems were expected.