The external morphology of Isomerocera Enderlein, an Afrotropical genus of Stratiomyidae, is discussed and illustrated with special regard to specific structures on the antenna, surface cover, and male and female terminalia. The species of Isomerocera are re-examined, based on 524 specimens (including four types) from 15 institutions, and two species were distinguished. The rare species I. heteraspis James, 1949 is characterised by some unusual autapomorphic characters. The common I. quadrilineata varies remarkably in colour characters, and the extent and density of hair patches. Isomerocera maculiventris (Macquart, 1850) is considered to be a junior synonym of I. quadrilineata (Fabricius, 1787) as is I. natalensis (Gerstaecker, 1857). Isomerocera quadrilineata var. melecta, as originally described by Speiser (1908), is identical with the nominal form. Generic characters are compared with the related genus Ptilocera from the Oriental and Australasian regions. Distribution data are summarised on the basis of the reliable published records and/or extensive material that we examined and collected in Angola, Burundi, Cameroon, Central African Republic, Democratic Republic of the Congo (Kinshasa), Equatorial Guinea, Gabon, Ghana, Ivory Coast, Kenya, Liberia, Malawi, Mozambique, Nigeria, Republic of the Congo (Brazzaville), Sierra Leone, South Africa, Tanzania, Togo, Uganda and Zimbabwe. I. heteraspis is known only from two localities in Burundi and Uganda. The known distribution of I. quadrilineata essentially covers the vast area of savannahs and the zone of lowland tropical moist broadleaf forests in Africa.