Two species of the lanternfish genus Hygophum, H. benoiti and H. hygomii, are present in the Mediterranean. Differentiation of the larvae from these two species has been problematic. An attempt to identify such larvae in the plankton samples of the North Western Mediterranean led to a broader study that included the examination of a large number of plankton samples collected in the region since 1976. The large number of Hygophum larvae obtained during July 1992 in the North Western Mediterranean (that proved to be H. benoiti), together with collections of larvae from different geographic areas (especially H. hygomii from the Southwest Indian Ocean), allowed a detailed morphometric comparison of the larvae of H. benoiti and H. hygomii. Developmental stages of H. benoiti from yolk sac to post-flexion larvae are described. Information on the temporal occurrence of H. benoiti in the plankton, as well as the spatial distribution of this species during the survey of peak abundance (June/July 1992) in the North Western Mediterranean, is presented.