The good genes mechanism of sexual selection predicts that secondary sexual ornaments may reliably reveal a males resistance to parasites. We studied correlates of courtship and spawning success in a species of Copadichromis, a lekking cichlid fish from Lake Malawi, Africa, which builds sand bowers. We present the first evidence of a negative relationship between the structure of an extended phenotypic character (height skew of sand bowers) and male parasite load. Males that spawned had significantly fewer dilepipid cestodes in their livers than males that did not spawn, never before demonstrated in a lekking species of fish. Furthermore, males that spawned had significantly heavier gonads than 'unsuccessful males. We also found significant correlations between relative liver weight and some measures of reproductive success. This may indicate females are choosing to mate with males in better condition. Copyright 1998 The Association for the Study of Animal Behaviour