The effect of spot asymmetry on female mate choice was investigated in the Trinidadian guppy, Poecilia reticulata. Spot asymmetry arises because whole pattern elements are missing from one side or are located in a different position on either side. Pairs of males were selected that differed in melanic spot asymmetry. In other respects the pair of males were matched for body size, display rate and other aspects of colour pattern. Two experiments were carried out, one in which asymmetry was caused by missing spot elements, the other in which asymmetry was caused by misaligned spots. The latter experiment does not confound differences of pigment area with differences in asymmetry. In both cases females strongly preferred the symmetric male. This was not sensitivity to fluctuating asymmetry (small differences in the size of spot areas) but to asymmetry at the gross level of spot pattern.Copyright 1997 The Association for the Study of Animal Behaviour