Background Existing theories suggest that the mother-infant relationship has a potentially significant effect on long-term adult mental health, but there are few empirical data to support this view. Even fewer prior studies have examined the specific dynamics of the mother-infant relationship and their association with adult mental health. Methods A total of 1752 inner-city infants born between 1960 and 1965 were followed prospectively as a part of the Collaborative Perinatal Project (CPP) and the Johns Hopkins Pathways to Adulthood Study. Multiple observations of development and an extensive adult interview were performed. Maternal behavior was observed and systematically rated at the infant's 4-month pediatric neurological evaluation and at 8 months by a developmental psychologist. Factor analysis was used to organize the maternal behavior variables into different types of dysfunctional mother-infant relationships. Adult mental health was assessed at the follow-up interview, when the infant had reached the age of 27-33 years, by the General Health Questionnaire (GHQ) and self-perception of current mental health. Results There was a significant association between unsupportive maternal behavior at 8 months and subsequent poor adult mental health (Fisher's exact test, p = 0.026). There was no association between overly involved maternal behavior and poor mental health as an adult. After adjustment for potential confounding variables, the elevated rates of poor adult mental health in children of mothers who exhibited unsupportive maternal behavior at 8 months persisted (OR = 1.41 [95% CI = 1.00-1.97], p < 0.05). Conclusion Infants who experience unsupportive maternal behavior at 8 months have an increased risk for developing psychological sequelae later in life.