Health care associated infections are considered as an indicator of quality and safety of health care institutions. The study aimed to determine the proportion of health care associated urinary tract infections, respiratory tract infections, surgical site infections, and to evaluate the association of medical devices and duration of hospitalization which predispose to health care associated infections. Four hundred and twenty three patients who stayed more than 48 hours or readmitted to surgical, medical, pediatric and gynecology wards in a tertiary care hospital in Sri Lanka during the study period were included in the study. Data extraction sheets were used and were filled with information obtained from bed head tickets and laboratory reports. A total of 79 (18.7%) patients had been diagnosed to have health care associated infection. The predominant type was respiratory tract infections 24 (30.4%) followed by urinary tract infections 21(26.6%), surgical site infections 17 (21.5%), and other infections 17 (21.5%). The highest proportion of urinary tract infections were seen in surgical wards (38.1%) whereas the highest proportion of respiratory tract infections were seen in medical wards (45.8%). Patients aged more than 60 were found to be affected most (27/94). Health care associated infections were significantly associated with usage of medical devices (p<0.05) and length of stay in hospital (p<0.05). The study concludes that these infections account for a noteworthy percentage in hospitalized patients and the predominant type was respiratory tract infections in this tertiary care hospital in Sri Lanka and elders were the mostly affected category compared to children and adults age groups.