Abstract: Models of inter-sexual selection generally assume heritable variation in mating preferences among females within populations. However, little is known about the nature of such variation. The aim of this study was to characterize quantitatively the phenotypic variation in female preference for a sexually selected male trait, body colour pattern, within a population of the Trinidadian guppy, Poecilia reticulata. Significantly more female guppies preferred the more brightly coloured of two similar-sized males presented simultaneously as potential mates. Mating preference scores for individual females were significantly and positively correlated between two repeated trials on successive days. Females were thus individually consistent in their particular choice of mates, and the calculated repeatability of their mating preference was relatively high. Notwithstanding the aforementioned, significant variation existed among females in the degree of their preference for brightly coloured males. Individual mating preference scores were not normally distributed, but were rather skewed to the right (i.e. towards greater values). These results suggest that additive genetic variation for mating preferences based on male colour pattern is maintained, and the opportunity for the further evolution of both bright male colour patterns and female preference for this trait appears to exist in the study population from the Quare River, Trinidad.