Hypertensive patients are at high risk of Drug therapy problems (DTPs) as they often receivedrnmultiple medications in order to achieve their target blood pressure. Currently studies concerningrnDTPs in patients with hypertension are limited in Ethiopia. Therefore, this study was aimed tornassess the magnitude of DTPs and contributing factors among adult ambulatory hypertensivernpatients in Ayder referral Hospital. Institution based cross sectional study was conducted amongrn384 study subjects who fulfilled the inclusion criteria. Trained data collectors collected the datarnfrom patient interview and chart review using structured data collection format. DTPs werernassessed using Cipolleâ€˜s classification system. Logistic and multivariate regression analysis wasrnperformed to identify factors associated with DTPs. Data were reported as mean and percentagernusing tables and figures. DTPs were found in 52.8% of study subjects. A total of 277 DTPs werernidentified from 203 study subjects in which, 1 DTP was identified from 133(65.5%) patients, 2 inrn66 (32.5%) patients and 3 in 4(1.97%) patients. The maximum number of DTPs found was 3 andrnthe average number of DTPs per patient was 1.36. Unnecessary drug therapy was the top leadingrn(32.5%) and dose too low (7.94%) was the least type of DTPs in the study subjects.ACEIs werernthe most frequent drugs involved in DTPs.The factor that was independently associated withrnDTPs was the total number of medications. The total number of medications taken by the patientrnper day was an important predictor of drug therapy problem AOR = 2.572 95% CI (1.062-6.229),rnP=0.01.