Background: One-person households are the most common type of household in Japan, but relatively little is known about the causes and potential consequences of the rise in solo living in young adulthood.

Objective: I address two questions: What accounts for the rise in one-person households in young adulthood? How is solo living in young adulthood related to well-being?

Methods: I use census data to evaluate how much of the growth in one-person households at ages 20−39 between 1985 and 2010 is explained by change in marital behavior and how much is explained by other factors. I then use data from the 2000−2010 rounds of the Japanese General Social Survey to examine whether and why men and women living alone differ from those living with others in terms of happiness and self-rated health.

Results: Results of the first set of analyses indicate that changes in marital behavior explain all of the increase in one-person households for men and three-fourths of the increase for women. Results of the second set of analyses indicate that those living alone are significantly less happy than those living with others, whereas the two groups do not differ with respect to self-rated health. The observed differences in happiness are not explained by differences in subjective economic well-being or social integration.

Conclusions: The relatively small magnitude of estimated differences in happiness and health provides little evidence to suggest that the projected rise in one-person households is likely to play a significant role in contributing to lower levels of well-being among young adults in Japan.