OBJECTIVES: To assess the effect of subcutaneous-allergen-specific-immunotherapy (SCIT) on disease severity classifications, number of days affected and sick days per year on patients with grass-pollen and/or house dust mite (HDM) induced allergic rhino-conjunctivitis (RC) and/or asthma (A). METHODS: A total of 248 patients started SCIT; an intension to treat approach was applied. The disease specific Rhino-conjunctivitis Quality of Life Questionnaire (RQLQ) and the two generic health-related quality of life (HRQoL) instruments 15D and EQ-5D were used. The outcome measures included change in; disease severity classifications, RQLQ-scores, number of days with symptoms, number of sick days, change in generic HRQoL and Quality-Adjusted-Life-Years (QALY). RESULTS: The disease severity classifications showed significantly improved disease control. Mean RQLQ-score was reduced from 3.02 at baseline to 2.00 at follow-up. Average annual days with symptoms were reduced from 189 days to 145 days whilst annual sick days were reduced from 3.7 to 1.2 days. The 15D-score increased from 0.83 to 0.86 and the EQ-5D-score from 0.70 to 0.77, which indicated an annual gain per patient of 0.03-0.06 QALY. CONCLUSIONS: Allergic patients suffering from RC alone or RC and A experience significantly increased HRQoL, when treated with SCIT for one year.