Sixteen older individuals with sleep maintenance insomnia were treated with night-time bright-light exposure (BL) while living at home. Twelve consecutive days of acute light treatment were followed by a 3-mo maintenance light-treatment period. Subjects completed laboratory evaluation sessions on five separate occasions (prior to and following the acute light-treatment period, and once per month during the maintenance period). During each laboratory session, performance levels, sleep, and core body temperature were measured. The performance battery consisted of four computerized tasks (Logical Reasoning, Stroop Congruency, Two Letter Visual Search, and Wilkinson Four-Choice Reaction Time) and was administered every 2 h between 10.00 and 18.00 hours. Subjects improved significantly on three of the four tasks from pre-BL to post-BL. During the maintenance period, subjects who received active BL treatment maintained significantly higher performance levels than a control BL group. Light treatment improved sleep efficiency and delayed the phase of the body temperature rhythm. Performance improvements were significantly related only to sleep and not to circadian phase. The implications for non-circadian treatments of sleep maintenance insomnia and cognitive functioning in the elderly are discussed.