Background. Opioid agonist treatment (OAT), for the treatment of heroin dependence, has been reported to improve overall health and lower mortality. Drug use and retention in treatment have often been used as measures of treatment success. More recently, however, researchers have suggested that measurements of quality of life should be an outcome in substance use treatment evaluations. In a recent randomized controlled trial we demonstrated high rates of successful rapid referral from a needle exchange program (NEP) to OAT. The aim of this study was to see whether an improvement in health related quality of life (HRQoL) could be seen at 3-month follow-up after starting OAT and whether it was associated with any baseline characteristics. We also wanted to compare our sample to a sample from the general population with regard to HRQoL. Methods. This was a 3-month follow-up of 71 patients who started OAT. Measurements of HRQoL with EQ-5D (an instrument developed by the EuroQol group) were made at baseline and at three months. Results. Mean EQ-5D VAS (visual analogue scale) for the study sample at baseline was 47.3, which was lower than a Swedish reference population reporting 83.3. Individuals reporting being prescribed a drug for a psychiatric condition had significantly lower EQ-5D index values. Improvement in EQ-5D index score was significantly less for individuals reporting previous overdoses (-0.10,