Oculotrema hippopotami Stunkard is a monogenean that is found around the nictitating membrane and under the eyelids of the hippopotamus. When specimens of O. hippopotami were collected from both eyes of 42 hippopotamuses in Uganda, 90.5% of the hippopotamuses were found to be infested. The maximum number of parasites on one hippopotamus was 41, and the mean number of parasites per hippopotamus was 8.26. The frequency distribution did not follow a Poisson distribution and is therefore considered to be non-random. Both mature and small immature worms were found in the same eye, therefore the infection does not immediately confer immunity on the host.