Objective Distribution of breast milk substitutes (BMS) after the 2006 Yogyakarta earthquake was uncontrolled and widespread. We assessed the magnitude of BMS distribution after the earthquake, its impact on feeding practices and the association between consumption of infant formula and diarrhoea among infants and young children.

Design One month after the earthquake, caregivers of 831 children aged 0–23 months were surveyed regarding receipt of unsolicited donations of BMS, and on recent child-feeding practices and diarrhoeal illness.

Setting Community-level survey in an earthquake-affected district.

Subjects Primary caregivers of surveyed children.

Results In all, 75 % of households with an infant aged 0–5 months and 80 % of all households surveyed received donated infant formula; 76 % of all households received commercial porridge and 49 % received powdered milk. Only 32 % of 0–5-month-old infants had consumed formula before the earthquake, but 43 % had in the 24 h preceding the survey (P < 0·001). Consumption of all types of BMS was significantly higher among those who received donated commodities, regardless of age (P < 0·01). One-week diarrhoea incidence among those who received donated infant formula (25·4 %) was higher than among those who did not (11·5 %; relative risk = 2·12, 95 % CI = 1·34, 3·35). The rate of diarrhoea among those aged 12–23 months was around five times the pre-earthquake rate.

Conclusions There were strong associations between receipt of BMS and changes in feeding practices, and between receipt of infant formula and diarrhoea. Uncontrolled distribution of infant formula exacerbates the risk of diarrhoea among infants and young children in emergencies.