Objective to evaluate the impact of social support on postnatal depression and health-related quality of life. Design prospective cohort study. Data were collected at baseline and at six weeks post discharge using a postal survey. Setting and participants between August and December 2008, 320 women from a large tertiary hospital were recruited following the birth of their infant. Measurements Edinburgh Postnatal Depression Scale (EPDS), Maternity Social Support Scale and World Health Organization Quality of Life assessment questionnaire. Findings of the 320 women recruited, 222 (69.4%) returned their six-week questionnaire. Women with low social support had significantly higher scores on the EPDS than women who reported adequate support (p=0.007). There was also a significant effect of social support on health-related quality of life. Women with low family or partner support scored lower in all domains, with the greatest mean difference in the social health domain (p=0.000). Of those scoring >10 on the EPDS, 75.5% had sought professional help. Conclusions and implications for practice women with low social support are more likely to report postnatal depression and lower quality of life than well-supported women. Careful assessment of a woman's level of support following the birth, particularly from her partner and family, may provide useful information for possible interventions.