Overweight [body mass index (BMI) percentile > or = 95th] in children has become a major public health problem. The age when overweight begins and how it progresses are mostly unknown. Such information would be important for the optimal timing of prevention. We conducted a survival analysis on time to overweight and compared survival curves by race and sex. Data from a cohort of 924 children recruited from schools in Indianapolis, IN, were analyzed. Blacks were at greater risk for becoming overweight than whites. Similar findings were obtained when at risk of overweight (BMI percentile > or = 85th and <95th) and overweight were considered as a single category. Twenty-five percent of blacks were overweight or at risk of overweight at or before age 7 yr, whereas it was age 11 yr in white females and age 10 yr in white males when 25% became overweight or were at risk of becoming overweight. The overall overweight-free survival curve for black females was significantly different from that for white females (P < 0.001), and black males were significantly different from white males (P = 0.04). There was no sex difference. The time to overweight during childhood and adolescence varies by race, indicating the need for race-specific timing of interventions.