Mental development of 4–5‐year old children on macrobiotic diets (almost devoid of animal foods and fat) with long‐term growth deficits, was studied using the Snijders‐Oomen Non‐verbal Intelligence (SON) scale. In addition, food consumption and behavioural style of the children, and family and parent characteristics were assessed. Parents were highly educated: 69% of the fathers and 47% of the mothers had completed college or university education. The children's energy intake was only 70% and calcium intake 40% of that reported for children of similar age on conventional diets. Fifteen out of 44 children (33%) did not complete the SON‐test, mainly due to difficulties in concentration. The non‐completers tended to score lower on parts of the SON‐test and the educational level of their fathers was slightly lower: no other differences were observed. Intelligence quotients (IQ) of the children who completed the test were high (IQ=126) compared to the reference population (IQ= 100 by definition). No significant relationship between IQ's and educational level of parents was observed, possibly due to lack of varation in educational level within the study population. Family size was inversely related with IQ. It was concluded that long‐standing mild to moderate malnutrition may not affect mental development in pre‐school children if the children grow up in a stimulating