Objectives: This study aimed to investigate solitary drinkers’ psychological problems such as perceived stress and depression, as well as their drinking motives and expectancies. Methods: The sample included 521 Korean adults who had experienced solitary drinking. They completed questionnaires measuring perceived stress level, depression, suicidal thinking, alcohol consumption in different contexts, and drinking motives and expectancies. Results: This study showed that people who engage in solitary heavy drinking only or both solitary and social heavy drinking are more likely to experience stress, depression, and suicidal thinking. While the enhancement motive was associated with amount of drinking in both solitary and social drinking groups, the coping motive was associated with amount of drinking only in the solitary drinking group. Conclusion: These findings suggest that people may drink alone to cope with their mental health problems such as stress and depression.