Child mortality in Tanzania rose from 137 per 1000 in 1992-1996 to 147 per 1000 in 1995-1999. Impact of HIV on child mortality is analyzed in a longitudinal community-based study in Kisesa ward, Mwanza region. HIV data on 4273 mothers from 3 rounds of serologic testing are linked to survival information for 6049 children born between 1994 and 2001, contributing 10,002 person-years of observation and 584 child deaths. Impacts of maternal survival and HIV status on child mortality are assessed using hazard analysis. Infant mortality for children of HIV-positive mothers was 158 per 1000 live births compared with 79 per 1000 for children of uninfected mothers; by age 5, child mortality risks were 270 per 1000 live births and 135 per 1000, respectively. Fifty-one deaths were observed among child-bearing women, 14 to HIV-positive mothers. Infant mortality among children whose mothers died was 489 per 1000 live births compared with 84 per 1000 for children of surviving mothers. Maternal death effects were statistically independent of HIV status. Allowing for age, sex, twinning, birth interval, maternal education, and residence, the child death hazard ratio for maternal HIV infection was 2.3 (1.7-3.3); hazard ratio associated with maternal death was 4.8 (2.7-8.4). The HIV-attributable fraction of infant mortality is 8.3% in a population in which prevalence among women giving birth is around 6.2%.