Data from a prospective multisite cohort study were used to examine the effect of HIV exposure, untreated HIV infection, and single-dose nevirapine on infant growth velocity. The 2009 WHO growth velocity standards constitute a new tool for this type of investigation and are in need of functional validation. In period 1 (3-24 wk), 65 HIV-infected, 502 HIV-exposed uninfected (HEU), and 216 HIV-unexposed infants were included. In period 2 (25-36 wk), 31 infants moved from the HEU group to the HIV-infected group. We compared weight velocity Z-scores (WVZ) and length velocity Z-scores (LVZ) by HIV group and assessed their independent influences. In period 1, mean WVZ (95% CI) was significantly (P < 0.001) lower in infected [-0.87 (-1.77, 0.04)] than HEU [0.81 (0.67, 0.94)] and unexposed [0.55 (0.33, 0.78)] infants. LVZ showed similar associations. In both periods, sick infants and those exposed to higher maternal viral loads had lower WVZ. Higher mean LVZ was associated with low birth weight. Infants that had received nevirapine had higher LVZ. In conclusion, HIV infection and not exposure was associated with low WVZ and LVZ in period 1. Eliminating infant HIV infection is a critical component in averting HIV-related poor growth patterns in infants in the first 6 mo of life.