Base line data together with data in public registers and a structured phone interview of 94 of the 121 non-attenders was used for an assessment of factors influencing participation in the prospective population study 'Men born in 1914' in Malmö, Sweden. The overall attendance rate was 80.5% but varied among areas in the city from 27% to 100%. The lower participation rate among single men remained, when correcting for social class, significant only for single men in social class III. Men who did not feel well and/or had been admitted to hospital during the last 12 months had a lower participation rate. A negative attitude towards health surveys in general was the most common reason for non-participation. The phone interview turned out to be a feasible method to reach non-attenders to assess whether the sample was representative of the population and to learn more about reasons for non-participation.