This study explored the effects of spouses' wake and sleep patterns on marital adjustment. A total of 150 couples from three states completed questions on wake/sleep patterns, marital interaction, marital adjustment, and problem solving. Couples whose wake and sleep patterns were mismatched (e.g., an evening person married to a morning person) reported significantly less marital adjustment, more marital conflict, less time spent in serious conversation, less time spent in shared activities and less frequent sexual intercourse than matched couples. Contrary to expectations for matched couples, night couples did not report more involvement in extra-familial social activities than morning couples. Morning couples engaged in sexual intercourse more frequently in the morning than night couples; night couples had sex more often in the evening than morning couples. There were no significant differences in the intercourse rates for morning couples and night couples. Compared to matched couples, mismatched couples with high marital adjustment reported more flexibility and adaptability in their marital problem solving. The implications of these findings for premarital counseling and marital therapy are discussed.