Background: Although poor maternal mental health is a major public health problem, with detrimental effects on the individual, her children and society, information on its correlates in low-income countries is sparse.

Aims: This study investigates the prevalence of common mental disorders (CMD) among at-risk mothers, and explores its associations with sociodemographic factors.

Methods: This population-based survey of mothers of children aged 0–36 months used the 14-item Shona Symptom Questionnaire (SSQ). Mothers whose response was “yes” to 8 or more items on the scale were defined as “at risk of CMD.”

Results: Of the 1,922 mothers (15–48 years), 28.8% were at risk of CMD. Risk of CMD was associated with verbal abuse, physical abuse, a partner who did not help with the care of the child, being in a polygamous relationship, a partner with low levels of education, and a partner who smoked cigarettes. Cohabiting appeared to be protective.

Conclusions: Taken together, our results indicate the significance of the quality of relations with one’s partner in shaping maternal mental health. The high proportion of mothers who are at risk of CMD emphasizes the importance of developing evidence-based mental health programmes as part of the care package aimed at improving maternal well-being in Tanzania and other similar settings.