Distribution of Rift Valley fever virus (RVFV) was studied in the mosquito Culex pipiens. Mosquitoes were dissected on days 1–7 after an infectious bloodmeal, and RVFV plaque assays were performed on the legs, posterior midgut, ovaries, salivary glands, thoracic ganglia, and remaining organs and tissues (remnants). On days 7–12 and 14 following an infectious bloodmeal, mosquitoes were tested for their ability to transmit virus and then dissected. Dissemination (systemic infection) rates averaged 22% on days 1–14 and transmission rates 33% on days 7–14. There were no significant differences in the viral titers of midgut samples among the nondisseminated infected (virus limited to alimentary canal), disseminated infected nontransmitting, and transmitting groups of mosquitoes. The sequence of infection of the organs and tissues studied appeared to be as follows: midgut, hemolymph, remnants; salivary glands, ovaries, and thoracic ganglia. Some individuals were found to have disseminated infections as early as 12 hr following an infectious bloodmeal. Trauma, simulated by vigorous shaking immediately following the viremic bloodmeal, did not affect either infection or dissemination rates.