OBJECTIVES: The aim of this study was to estimate the impact of pandemic Influenza A H1N1/2009 in terms of patient’s health care services utilization, work absenteeism and associated costs. METHODS: Longitudinal, descriptive, multi-centre study of in- and outpatients with confirmed diagnosis of influenza A H1N1/2009 in Spain. Sociodemographic and clinical characteristics were gathered together with health and social resources use, at the admission or primary visit, and also after recovery. Cost analyses were conducted under a social perspective, incidence focus and with a temporal horizon of 3 months. Unit cost of resources was imputed to calculate the mean cost by inpatient and outpatient. A sensitivity analysis with variations was conducted (Monte Carlo simulation). RESULTS: A total of 172 inpatients and 224 outpatients were included, 20% and 30% of whom, respectively, were under 17 years old; 12% of inpatients were at ICU, 7.8 (SD=3.7) days, on average, and stayed in general wards for 9.6 (SD=7.7) additional days. The rest of inpatients had a mean hospitalization length of 5 (SD=4.4) days. The most frequently used ambulatory health resource was the primary care medical assistance; 43.8% of inpatients and 66.1% of outpatients were employed, of whom 100% (inpatients) and 91.7% (outpatients) went on sick leave. Absenteeism length was of 30 (SD=20.7) days for inpatients and 9 (SD=6.3) for outpatients. Caregivers of 21.7% of the inpatients also led work absenteeism, as well as the 8.5% of those of outpatients. The proportion of indirect cost for general-ward-inpatients was 30%. This percentage ascended to 77% in the case of outpatients. The mean costs per inpatient were €6,236 (CI95%=1,384–14,623) and €940 (CI95%=66–3,064) per outpatient. CONCLUSIONS: Hospitalizations represents the highest economic cost, together with work absenteeism. Since only a marginal proportion of influenza cases are hospitalized, productivity losses emerge as the most important impact of the disease.