BACKGROUND: Kenya is a high HIV high burden country, the epidemic is a major cause of premature death accounting for 29% of annual adult deaths, 20% of maternal mortality and 15% of deaths in children under the age of five in 2013. It also has lowered the per capita output by 4.1%. Antiretroviral treatment (ART) is the main intervention being implemented to mitigate these impacts. The the demand for ART has continued to increase, implying increase in the cost of treatment. Studies on service provision and cost of HIV treatment are limited in Kenya. OBJECTIVES: The objective of this research was to estimate quantity of resources utilized and costs for adults initiating ART. METHODS: Data on resource utilization including ARV and non-ARV drugs, laboratory tests, imaging procedures, outpatient and inpatient services, fixed costs and retention in care were retrospectively extracted from the medical charts of 330 patients who were initiated on ARVS  (18) between 2003 and 2010, in Mbagathi District Hospital, Kenya. The unit costs were estimated from the providers’ using micro costing and gross costing methods. RESULTS: Average number of outpatient visits per patient during the first treatment quarter was 4.37, and 13 and 10 for year 1 and year 2 respectively. The average outpatient cost of treatment was Ksh9044 (USD121) for quarter 1 and was Ksh6500 (USD87) and to Ksh5800 (USD77) for year 1 and year 2 respectivel. The total cost per inpatient day was estimated at KSh1691 (USD23). The undiscounted lifetime costs and life benefits of ART were Ksh932,071 (USD1,245) and 16 years respectively. CONCLUSIONS: The outpatient costs were highest in the first quarter of treatment and significantly reduces during the subsequent periods. The service provision especially laboratory tests are offered on need basis and not regularly are recommended by treatment guidelines.