We evaluated the association between the severity of primary human immunodeficiency virus type 1 (HIV-1) illness and HIV-1 plasma virus load before seroconversion using stored plasma samples obtained from 74 prostitutes in Mombasa, Kenya. Fever, vomiting, headache, fatigue, arthralgia, myalgia, sore throat, skin rash, or being too sick to work were each associated with significantly higher virus loads before HIV-1 seroconversion, and each additional symptom or sign was associated with an increase in virus load of 0.4 log(10) copies/mL.