The objective of this study was to assess the impact of high levels of insomnia on response to pregabalin (PGB) in patients with generalized anxiety disorder (GAD). Pooled data were analyzed from six double-blind, placebo-controlled, 4- to 6-week trials of outpatients who met the Diagnostic and Statistical Manual of Mental Disorders (fourth edition) criteria for GAD with a minimum Hamilton Rating Scale for Anxiety (HAM-A) score = 18. Response was evaluated for three fixed-dose PGB groups (150, 300-450, 600 mg/day), and for a benzodiazepine group (alprazolam or lorazepam). A 'high-insomnia' subgroup was defined by a baseline HAM for Depression (HAM-D) insomnia factor score greater than 3 (maximum = 6). At baseline, 1002 (54%) patients met the criteria for the high-insomnia subgroup, and 852 (46%) for the low-insomnia subgroup. Mean baseline HAM-A scores were 1-2 points higher in high-insomnia versus low-insomnia patients. In high-insomnia patients, PGB produced significantly greater improvement in HAM-A total scores at last observation carried forward endpoint on 300-450 mg (-13.1+/-0.6) and 600 mg (-11.2+/-0.5) dose groups compared with placebo (-8.3+/-0.5; P<0.0001 for both comparisons); the improvement on PGB 150 mg was not significant (-9.9+/-0.7; P = 0.051). Improvement was significant in the benzodiazepine group (-11.0+/-0.6; P<0.0001). In the high-insomnia subgroup, treatment with PGB significantly (P<0.001) improved the HAM-D insomnia factor scores on both the 300-450 mg (-2.73) and 600 mg (-2.35) doses, and on benzodiazepines (-2.52) compared with placebo (-1.51); improvement on PGB 150 mg (-1.69) was not significant. Rates of treatment-emergent insomnia were lower on PGB compared with placebo in both the high- and low-insomnia subgroups. In conclusion, PGB was well tolerated, and improved overall anxiety symptoms, while specifically improving insomnia in patients with GAD presenting with high levels of concurrent insomnia.