Increased nutritional needs in adolescence due to increased growth rate and body composition changes associated with puberty coincides with other factors that affect adolescents' food choices, nutrient intake, and consequently, nutritional status. Improper food choice results in malnutrition with its grave consequences. This study was carried out to assess the nutrition knowledge, dietary diversity and nutritional status of adolescents in three Local Government Areas (LGAs) of Ibadan municipality, Oyo State; Nigeria. The descriptive cross-sectional study was carried out among 450 In-school (ISA, 225) and Out-school (OSA, 225) adolescents aged 10-19 years randomly selected from three out of five LGAs. Fifteen secondary schools were randomly selected from the three LGAs. The ISA were selected through systematic random sampling technique, while OSA were recruited from markets, motor parks, mechanic workshops, and shops with adolescent apprentices through snowball technique. Semi-structured, interviewer-administered questionnaire was used to collect data from the respondents. Data were analyzed using descriptive statistics, ANOVA and Chi-square test at p = 0.05. More than half (58.7%) of respondents had poor nutrition knowledge, 70.0%, 28.7% and 1.3% had high, average and low dietary diversity score, respectively, 92.8% had normal height-for-age, 5.7% were mildly stunted and 1.5% severely stunted. Majority (87.3%) of the respondents had normal BMI-for-age, 7.3% were underweight and 4.9% were overweight. No significant correlation was found between BMI-for-age and nutrition knowledge of respondents. The BMI-for-age of In-school adolescents was negatively correlated with dietary diversity scores. In-school respondents had good nutrition knowledge which did not translate to good food habit, while out-of-school respondents had poor nutrition knowledge and good food habit. There is need for nutrition education in the nation's secondary schools and enlightenment programme for out-of-school adolescents about importance of good nutrition to growth and development.