It is a common practice for young adults to delay their weekend sleep schedule. The present study was designed to assess the effect of this sleep pattern on the sleep of Sunday night and the functioning of Monday morning. The sleep schedules of 30 young adults were manipulated for 2 consecutive weeks. In the Habitual-Sleep (HS) week, subjects followed their habitual sleep schedule throughout the week; in the Delayed-Sleep (DS) week, subjects' sleep schedule on Friday and Saturday nights were delayed by two hours. Compared to the HS week, subjects showed significantly lower subjective sleepiness near bedtime and trends of longer sleep onset latency on Sunday night in the DS week. In addition, there was both lowered cognitive performance and overall mood rating on Monday morning in the DS week. The delayed weekend sleep pattern contributes to Sunday night insomnia and the Monday morning “blues”.