BACKGROUND: Drug therapy problems (DTPs), with the associated risks inherent in antihypertensive and antidiabetic therapy require utmost attention.  OBJECTIVES: To assess the DTPs observed in the management of hypertension and diabetes mellitus (DM) in two tertiary health facilities in Niger Delta region of Nigeria.  METHODS:  In a retrospective study, 531 randomly selected case notes of hypertensive and/or diabetic patients who attended the health facilities in 2011 and 2012 were evaluated for DTPs using Beer’s/STOPP/START criteria and selected guidelines in elderly and the general patients respectively. Data collected were analyzed with the aid of Statistical Package for Social Sciences version 20.0 and GraphPad Instat version 3.10 for windows (GraphPad Software, San Diego California USA) and presented using descriptive statistics.  RESULTS: The mean patients’ age was 55.70±12.23 years with the elderly patients constituting 70.2% of the population studied. Overall, average numbers of drugs prescribed per prescription in the first-month and the fourth–month period of drug therapy considered were 4.91±1.96 and 4.92±1.70 (p>0.05) with associated mean DTPs values of 1.54±1.08 and 1.46±1.20 (p>0.05) respectively. Using Beer’s/STOPP/START criteria, 21.5% and 22.8% of all DTPs at therapy initiation and last clinic visit were identified in the old patients. Unnecessary drug therapy was the most observed DTP in the first month (23.6%) and last fourth-month (29.4%) period of therapy in all the patients and was closely followed by wrong drug therapy (23.4%, 22.9%), need for additional drug therapy (20.9%, 17.4%), non-adherence to drug therapy (15.4%, 13.8%), and drug interactions (12.9%, 9.6%). Other DTPs observed, though to lesser extents were dosage too low (1.5 %, 5.2 %), adverse drug reaction (1.4 %, 1.3 %) and dosage too high (0.9 %, 0.4 %) respectively.  CONCLUSIONS: There was high incidence of DTPs in the hypertensive and/or diabetic patients. Unnecessary drug therapy and wrong drug therapy were the most frequently observed DTPs.