We have assessed the efficacy of anti retroviral therapy (ART) using undetectable viral load (VL) (<50 RNA copies/ml) as a marker of virological success, in patients who have Human Immunodeficiency Virus (HIV) attending the Department of Infectious Disease. A cross-sectional review of patients' case notes was used to obtain their demographics and treatment details. 79% (253) of the hospital case notes of clinic population was available for analysis, which represents 90% of those receiving ART in the clinic. 166/253 of the cohort were receiving treatment at the time of this study and 95% (157/166) of these were on treatment for greater than 6 months. The total virological success rate is 93%, which is comparable to other centres and are as good as those from published clinical trials. 56% of those on therapy who have virological failure were Intravenous Drug Users (IVDUs). Case by case investigation for those with treatment failure is warranted.