In Denmark influenza vaccinations are usually paid for by the patients. In the autumn of 1996 Copenhagen City Council offered free influenza vaccinations to all residents aged 70 years or older. The impact of the campaign was evaluated in a questionnaire study of a random sample of the Danish population aged 70 years or older. In Copenhagen 81% (95% Confidence interval: 67-95%) of the elderly at risk were vaccinated compared to 51% (45-56%) outside Copenhagen. Offering free influenza vaccinations in a mass campaign is an effective way of improving coverage rate. However, no substantial difference was found in cost between the mass campaign and a targeted campaign with free vaccination in general practice.