Full-sib heritabilities, phenotypic and genetic correlations of 10 morphological and three life history traits in the European dung fly Sepsis cynipsea are presented. We further supply a within-species test of Cheverud's (1988) conjecture that phenotypic correlations may be good, and much easier to obtain, substitutes for genetic correlations. Males were smaller in all traits except fore femur width. Heritabilities of morphological traits ranged from 0.33 to 0.90 and tended to be higher than the average reported for ectotherms ( Mousseau & Roff, 1987). Those for the three female life history traits estimated were lower (0.16–0.32) and about average. Genetic correlations between the sexes ranged from 0.52 to 0.87 and were all less than unity. Differential selection on morphology in males and females can thus be expected to produce fast evolutionary responses in this species. Our analysis revealed also that in S. cynipsea phenotypic correlations are good substitutes for genetic correlations for combinations involving morphological traits, and that genetic correlations derived from the ancova and the family mean methods were very similar. However, the former correspondence may be strongly reduced by the inclusion of particular traits (here male seta length).