Although several factors condition mental health differences between married and never-married adults, given recent increases in marriage delay and permanent singlehood, one modifying factor--deviation from desired age at marriage--has yet to be examined. Using data from the National Longitudinal Survey of Youth 1979 (N = 7,277), the author tested whether deviation from desired age at marriage shapes the mental health of married and never-married adults as well as mental health differences between them. The results showed that most respondents failed to meet their initial preference for age at marriage. Marrying both earlier and later than desired (compared to on time) resulted in poorer mental health and fewer benefits compared to never marrying. For the never-married, mental health was best, and differences compared to the married were nonsignificant, for those nearest their desired age at marriage. As timing deviations increased, however, a mental health deficit among the never-married emerged. (Contains 4 tables and 2 figures.)