The prevalence of obesity among American children and adults has increased substantially over the past few decades. This research used an ecological framework to examine the relationships between biological, dietary, sociocultural and behavioral factors to determine how these factors influenced obesity status during adolescence in West Philadelphia. Correlates, values, and health risks of obesity were addressed. In Phase I of the study, obesity-related attitudes, anthropometric, dietary, and sociodemographic factors were measured for 392 West Philadelphia adolescents (11-15 years). Data were compared to two other groups of Philadelphia adolescents of comparable socioeconomic status and ethnic background measured in the 1960s and 1970s. Phase II was based on 32 matched-pairs of obese (BMI and triceps skinfold $\ge$95th percentile of NHANES I) and non-obese (BMI and triceps skinfold between the 15th and 85th percentiles of NHANES I) female adolescents selected from the Phase I sample based on obesity status and matched according to stature and age. Adolescents were compared on the following measures: physical activity, sedentary behavior, dietary intake, eating attitudes, health behavior knowledge, body image, self-esteem, and maturation status. Findings from Phase I include a threefold increase (males) and a fourfold increase (females) in the prevalence of obesity over the last two decades that was not concurrent with an increase in body fat centralization. The West Philadelphia adolescents had macronutrient intakes that were higher than the RDA and higher than age- and sex-specific data from NHANES III (Life Sciences Research Office, 1995). Micronutrient status was excellent, with the exception of calcium, zinc, fiber, and vitamins A and D. In Phase II, physical activity and television watching emerged as the most important contributory factors to obesity status. There were no statistically significant matched-pair differences in macronutrient and micronutrient intakes, self-esteem, eating attitudes, health behavior knowledge, body image, or maturation status of these adolescents. Findings indicate that sociocultural factors in the urban environment may promote obesity for these adolescents. This research suggests that future intervention strategies include attention to physical activity, television watching habits, and sociocultural factors in the urban environment.