Anticoagulant therapy is one of the most common form of medical treatment. The most commonrnanticoagulant therapy complications are bleeding and thromboembolic complications. Bleeding isrnthe primary complication. Factors that can affect the complications include age, gender,rncomorbidities, intensity of anticoagulant effect, length of therapy and concomitant drugs. Thernobjective of the study was to assess complications of anticoagulant therapy at medical wards ofrnTikur Anbessa Specialized Hospital. A prospective longitudinal study design involving patientrnfollow-up and chart review was conducted from November to June 2014. Chi-square test andrnLinear Mixed Model regression were employed to examine the relationships and associationsrnbetween variables. The incidence of complications of anticoagulant therapy was found to be 60rn(26%). Bleeding was the most common reported 27 (12.4%) (5.2% major, 10.7% minor), followedrnby thromboembolism 12 (7.1%), bruising 10 (5.9%), heparin induced thrombocytopenia 9 (5.3%)rnand skin necrosis 8 (4.7%). Sex, concomitant drugs, intensity of INR/aPTT values, usual trend ofrncoagulation treatment and having coagulation profiles from different laboratory sites had beenrnassociated with complications. However, age, comorbidities, length of therapy, number ofrnanticoagulants and anticoagulant therapy related factors were not significant risk factors. Thernfindings of this study indicated that patient on anticoagulant therapy at medical wards were at higherrnrisk of bleeding followed by thromboembolic complications. Availability of coagulation laboratoryrnreagents at Tikur Anbessa Specialized Hospital and preparing guidelines on anticoagulant therapyrnharmonized with the laboratory values is recommended.rnKey words: Complication, bleeding, thromboembolism, skin necrosis, bruising, HIT, INR,rnaPTT, anticoagulants