Broad-sense heritability of fluctuating asymmetry and developmental instability in the winter moth were analysed in a full-sib breeding experiment. Effects of both genetic background and common environment on both tibia FA (measured for the three pairs of legs) and body size were studied. As body size has previously been shown to be a reliable indicator of larval feeding success and expected fitness, the relationship between FA and body size was investigated as well. This relationship is of interest because it has been argued that the low heritability of FA results from a strong relationship between FA and fitness. Broad-sense h2 of body size equalled zero whereas the effect of common environment was strong. The heritability of FA was low and not statistically significant for separate tibias. For FA based on the average of the three tibias h2 equalled 0.07 and differed significantly from zero. The heritability of developmental instability equalled 0.09. Thus the use of the hypothetical repeatability to translate the h2 of FA to h2 of developmental instability did not result in a strong increase in this species. Individual asymmetry was not correlated with fitness (as estimated by body size), indicating that the low heritabilities of FA are not a consequence of a strong correlation with fitness. Between-trait correlations in the unsigned FA were significant. However, these correlations are not necessarily indicative of an individual asymmetry parameter as the signed FA values were positively correlated as well, suggesting interdependent development of the three pairs of legs. Further research is necessary to investigate what the effects of interdependent development are on patterns in FA.