OBJECTIVES: To assess if there is any association between hyperemesis gravidarum (HG), psychological morbidity and infant bonding and to quantify any psychosocial consequences of HG. DESIGN: Two-point prospective case-control, multicentre survey study with antenatal and postnatal data collection. SETTING: Three London hospitals. PARTICIPANTS: Pregnant women at ≤12 completed weeks gestation recruited consecutively over 2 years. Women with HG were recruited at the time of admission; controls recruited from a low risk antenatal clinic. 106 women were recruited to the case group and 108 to the control. Response rates at antenatal data collection were 87% and 85% in the case and control groups, respectively. Postnatally, the response rate was 90% in both groups. PRIMARY AND SECONDARY OUTCOME MEASURES: Primary outcomes were psychological morbidity in the antenatal and postnatal periods, infant bonding in the postnatal period and psychosocial implications of HG. Secondary outcomes were the effects of severity and longevity of HG and assessment of correlation between Edinburgh Postnatal Depression Scale scores and maternal-to-infant bonding scores. RESULTS: Antenatally, 49% of cases had probable depression compared with 6% of controls (OR 14.4 (5.29 to 39.44)). Postnatally, 29% of cases had probable depression versus 7% of controls (OR 5.2 (1.65 to 17.21)). There was no direct association between HG and infant bonding. 53% of women in the HG group reported needing four or more weeks of sick leave compared with 2% in the control group (OR 60.5 (95% CI 8.4 to 2535.6)). CONCLUSIONS: Long-lasting psychological morbidity associated with HG was evident. Significantly more women in the case group sought help for mental health symptoms in the antenatal period, however very few were diagnosed with or treated for depression in pregnancy or referred to specialist perinatal mental health services. HG did not directly affect infant bonding. Women in the case group required long periods off work, highlighting the socioeconomic impact of HG.