<i>Background</i>: Non-communicable diseases (NCDs) are the leading causes of poor health and premature mortality worldwide. Although NCDs are majorly prevalent in middle to late adulthood, most lifestyle habits are started during adolescence a significant period of development. This research evaluated the risk and determinants of non-communicable diseases among adolescents in public and private secondary schools in Port Harcourt, Rivers State. <i>Methods</i>: The study used a comparative cross-sectional design to collect research data from 640 adolescents. Participants were selected through a multi-stage sampling technique and data was analysed with IBM Statistical Product for the Service Solution version 29. <i>Results</i>: Private and public school respondents report on NCDs (asthma, diabetes and high blood pressure) was 3.4% and 2.5% respectively. NCDs behavioural and metabolic risk factors were prevalent among both private and public school adolescents. Private school students exhibited higher prevalence of physical activity (75% vs. 61.6%), soft drink consumption (96.3% vs. 92.5%), alcohol consumption (45.6% vs. 36.9%), overweight (17.3% vs. 7.5%), obesity (5.9% vs. 1.6%), prehypertension (12.8% vs. 5%) and hypertension (6.6% vs. 1.6%). Conversely, public school students had higher prevalence of daily fruit intake (19.4% vs. 8.8%) and tobacco use (7.5% vs. 2.2%). Socioeconomic status, behavioural risk factors and metabolic risk factors were statistically significant (p<0.05). <i>Conclusion</i>: This study identified NCDs risk factors among adolescents that can lead to development of NCDs in adulthood, hence there is need for preventive measures that are targeted and data-driven to ensure adolescents adopt healthy lifestyles.