Identification of Simulium damnosum s.l. vectors of onchocerciasis demands adequate knowledge of the chromosomal features that distinguish human-biting members from nonanthropophilic forms. In this study, 955 S. damnosum larvae collected from various geographical locations in Tanzania were chromosomally analyzed. 358 larvae from small mountain streams in the northeast and central regions of Tanzania, were identified as mainly Nyamagasani and Sanje forms, with only one Kiwira form. 378 larvae from plain and lowland rivers, also in the northeast and central regions, were identified as Nkusi, Kisiwani and Kibwezi forms. Chromosomal examination of 219 larvae from the southern highlands zone revealed the presence of Kiwira and Nyamagasani forms. A further 27 larvae of S. damnosum complex collected from 5 rivers in Uganda were identified as Sebwe and Nkusi forms. Chromosomal photomicrographs on which the distinguishing characters were based are provided. These observations are discussed in the light of previous studies carried out on the S. damnosum cytological forms in Eastern Africa.