We report a 25 year-old patient with seasonal affective disorder (SAD) and cocaine abuse who experienced cyclical fluctuations in cocaine craving which were concomitant with seasonal alterations in mood. The temporal association of both disorders in this patient suggests that they may share a common underlying pathophysiology. Since disturbances in circadian rhythms and pineal melatonin functions may in part underlie the pathophysiology of SAD and the psychomimetic effects of cocaine are mediated in part through the pineal gland, we propose that dysfunction of circadian rhythms and pineal melatonin functions may partly mediate the association of SAD with cocaine abuse. This hypothesis may have potential clinical and therapeutic implications for a subgroup of cocaine abusers with SAD since light therapy, which is efficacious in the therapy of SAD, may also prove to be beneficial in reducing cocaine addiction. Furthermore, the report illustrates the need for investigations of environmental cues for cocaine abuse with specific attention given to the effects of light on circadian mood changes.