Trazodone is prescribed widely as a sleep aid, although it is indicated for depression, not insomnia. Its daytime cognitive and psychomotor effects have not been investigated systematically in insomniacs. The primary goal of this study was to quantify, in primary insomniacs, the hypnotic efficacy of trazodone and subsequent daytime impairments. Sixteen primary insomniacs (mean age 44 years) participated, with insomnia confirmed by overnight polysomnography (sleep efficiency ≤ 85%). Trazodone 50 mg was administered to participants 30 min before bedtime for 7 days in a 3-week, within-subjects, randomized, double-blind, placebo-controlled design. Subjective effects, equilibrium (anterior/posterior body sway), short-term memory, verbal learning, simulated driving and muscle endurance were assessed the morning after days 1 and 7 of drug administration. Sleep was evaluated with overnight polysomnography and modified Multiple Sleep Latency Tests (MSLT) on days 1 and 7. Trazodone produced small but significant impairments of short-term memory, verbal learning, equilibrium and arm muscle endurance across time-points. Relative to placebo across test days, trazodone was associated with fewer night-time awakenings, minutes of Stage 1 sleep and self-reports of difficulty sleeping. On day 7 only, slow wave sleep was greater and objective measures of daytime sleepiness lower with trazodone than with placebo. Although trazodone is efficacious for sleep maintenance difficulties, its associated cognitive and motor impairments may provide a modest caveat to health-care providers.