In a prospective study of 1002 pregnant, HIV-1 infected Tanzanian women, we examined the incidence of fetal death, preterm delivery, low birth weight (LBW), and small for gestational age (SGA) births in relation to maternal anthropometry at the first prenatal visit, weight loss, and low weight gain during pregnancy. Anthropometric measurements were obtained monthly during the 2nd and 3rd trimesters. Low maternal height and weight at the first visit were significantly related to lower mean birth weight and increased risk of SGA, but not to preterm delivery. Maternal stature < 150 cm was significantly related to fetal death. Weight loss during pregnancy, defined as a negative slope of the regression of weight measurements on the week of gestation, occurred in 10% of the women. It was related to increased relative risk (RR) of fetal death (RR = 1.83, 95% CI = 0.93, 3.57), preterm delivery (RR = 1.85, 95% CI = 1.40, 2.44), and LBW (RR = 2.85, 95% CI = 1.69, 4.79) after adjusting for multivitamin supplementation, height, primiparity, baseline weight, malaria, CD4 cell count, HIV disease stage, and intestinal parasitoses. The significant association with fetal death was stronger for weight loss during the 2nd trimester, whereas increased risks of preterm delivery and LBW were higher for weight loss during the 3rd. Similar but weaker associations were found with low weight gain during pregnancy (slope < 25th percentile). We conclude that poor anthropometric status at the first prenatal visit and weight loss during pregnancy among HIV-1 infected women are strong risk factors for adverse pregnancy outcomes. J. Nutr. 134: 1424-1431, 2004.