Objective: Lifestyle modification is an essential component of self-management of diabetes mellitus. This study assessed adherence to diet and exercise recommendations and elucidated the factors that influence adherence in patients living with diabetes. Method: A cross-sectional study involving 300 patients attending diabetes clinics in some selected hospitals in Ogun State, Nigeria. Structured questionnaires were used to obtain information on the socio-demographic characteristics, and PRECEDE factors of lifestyle-modification adherence in the study participants. Pearson’s correlation and Chi-square test were used to assess the association between the variables, while binary logistic regression was used to determine the predictors of adherence to dietary recommendations. Results: The mean age of the study respondents was 62.7 years. The proportion of respondents who adhered to dietary and exercise recommendations were 87.8% and 45.6% respectively. There were no statistically significant linear relationships between scores for each PRECEDE factor and scores for adherence to diet and exercise. Respondents’ age, body mass index, and duration of illness had a statistically significant association with adherence to diet (P< 0.001, P=0.021, and P=0.041 respectively). On logistic regression analysis, participants 60 years and older had a higher likelihood of adhering to dietary modification than younger participants [AOR=2.6, P < 0.001]. Conclusion: The adherence of patients living with diabetes to dietary recommendations was satisfactory while adherence to exercise recommendations was very poor. There is a need for health care workers, especially at the primary and secondary levels to implement strategies that will enhance reinforcing and enabling factors for exercise adherence.