Background: This study aimed to clarify the differences in drinking norms and motives among different groups (non/light, solitary, and social drinkers) in a representative sample of Korean adults. We also examined which group—solitary or social drinkers—was more likely to engage in heavy drinking. Methods: The study used nationwide cross-sectional data collected in 2018. A total of 3,000 subjects aged 19 to 60 years were sampled for this study, including 1,532 men and 1,469 women. The data were analyzed with SPSS 23.0. Results: Solitary drinkers are more likely to be divorced or separated, less educated, and marginally employed (people with temporary jobs, rather than regular; the self-employed; and people with service- and sales-related jobs). Solitary drinkers peaked in their 30s (18.5%) and social drinkers in their 50s (68.1%). Solitary drinkers drank more frequently than social drinkers (Mean=6.1 vs. 3.6 per month, p<.001) and consumed a significantly larger quantity of alcohol (Mean=69.5 g vs. 46.8 g per week). S olitary drinkers were more accepting of drinking-related behaviors in a variety of situations than were social drinkers. The regression analysis revealed that personal motives for drinking were the most important factor of drinking frequency and drinking consumption for both solitary and social drinking. Conclusion: These findings suggest that people who drink alone may be more vulnerable to alcohol abuse than social drinkers.