To evaluate whether, at the community level, diarrhoea is a major cause of malnutrition or inversely whether the association between diarrhoea and growth retardation can be explained by a higher susceptibility of malnourished children to diarrhoea, all recent studies examining the relationship between diarrhoea and malnutrition in the community were reviewed. It was determined, for each of these two hypotheses, to what extent four standard causality criteria were met, viz., (i) lack of temporal ambiguity, (ii) consistency of findings, (iii) strength of association and (iv) biological plausibility. That malnutrition predisposes to diarrhoea seems likely: this is supported by a series of studies which adequately fulfil the examined causality criteria and seems biologically plausible. On the other hand, it is not clear whether diarrhoea is a major cause of malnutrition. Some studies examine the effect of diarrhoea on nutritional status over short time intervals and it cannot be determined whether diarrhoea-induced growth faltering is transient or sustained. Other studies examining this effect over longer periods do not show clearly that diarrhoea precedes malnutrition. Inconsistencies between studies and lack of evidence supporting a biologically plausible mechanism also question the importance of diarrhoea as a cause of malnutrition.