Sleep disturbances play an important role in the exacerbation of pain and other troubling symptoms reported by patients with fibromyalgia (FM). The objective of this trial was to analyze the efficacy of a cognitive-behavioral therapy for insomnia (CBT-I) versus a sleep hygiene (SH) education program at improving sleep and other clinical manifestations in FM. Sixty-four FM women with insomnia were randomly assigned to the CBT-I or the SH groups, and 59 completed the treatments (30 in the CBT-I group and 29 in the SH group). Participants completed several self-report questionnaires at pre-, post-treatment and follow-ups. The CBT-I group reported significant improvements at post-treatment in several sleep variables, fatigue, daily functioning, pain catastrophizing, anxiety and depression. The SH group only improved significantly in subjective sleep quality. Patients in the CBT-I group showed significantly greater changes than those in the SH group in most outcome measures. The findings underscore the usefulness of CBT-I in the multidisciplinary management of FM.