The postnatal period is a time of increased stress and sometimes high levels of anxiety and depression for mothers. While there has been substantial research on postnatal mental health problems and interventions, very little is known about the transition to work after maternity leave, and how work interacts with perinatal emotional distress. This work investigates how the mental health of mothers who are returning to work relates to their demographic characteristics as well as the interpersonal and administrative features of their work. These data were gathered with a comprehensive questionnaire that measured demographics, levels of distress, work characteristics, presenteeism, illness disclosure, co-worker support, manager support, and job quality. A total of 246 working mothers from New Zealand with children under 24 months old were included in the sample. The sample showed significantly higher levels of distress on the Depression, Anxiety, and Stress Scale (DASS-21) than the normative population. Education level and financial situation were negatively correlated with DASS-21 scores, and the experience of previous perinatal distress (PND) and working from home were positively associated with DASS-21 scores. Presenteeism, attitudes to illness disclosure, and co-worker support all had medium strength significant correlations with DASS-21 scores, while manager support showed a weak significant correlation with the DASS-21. A t-test showed that mean DASS-21 scores of Māori mothers were significantly higher than those of Pākehā mothers. Co-worker support, financial situation, being Māori, and job location all contributed significantly to the variance of DASS-21 scores within the full sample. Presenteeism, attitude to illness disclosure, and co-worker support all contributed to the variance of DASS-21 scores for the sub-sample that reported experiencing PND. These findings provide evidence that work related factors should be a focus in further research into perinatal distress. Future research might also explore these factors in a larger, more diverse sample to allow for examination of the experiences of mothers from a variety of ethnic, cultural, vocational, and socioeconomic groups.