The major approach to patients? health problems is the use of drugs particularly in the co morbid states. In this study we intend to evaluate the prescribing pattern, determine the nature and extent of irrational drug use and assess rate of medication adherence and reasons for non adherence among patients attending an outpatient clinic of Olabisi Onabanjo University Teaching Hospital (OOUTH) Sagamu, Ogun State, Nigeria. A two fold study was done using 100 case notes belonging to diabetic hypertensive patients of whom 67 patients were available for oral interview on medication adherence. Data on sex, age, groups of medicines prescribed, number of prescriptions and number of medicines occurring per prescription were obtained, World Health Organization (WHO) prescribing indicators were calculated and occurrence of irrational prescribing was detected. Analysis was done using Microsoft Excel 2000. Female to male ratio was 1:0.59 and average age + SD of the patients was 63+10 years. Anti diabetics were the most prescribed medicines 1152(31.8%) followed by anti-hypertensives 865(23.9%). Average no of drugs per prescription was 4.7; Percentage of drugs prescribed as generics 40.1%; Percentage of antibiotics and injections per prescription were 9.4% and 2.1% respectively. Extravagant prescribing occurred in 92.7% of the cases. Forty nine (73.1%) were adherent. Cost (63.2%) and forgetfulness915.7%) were reasons for non adherence. Prescribing in this group of patients is sub-optimal, however majority claimed to be adherent. Interventions are needed for health care providers and the patients alike.