Changes in smoking and drinking habits of fathers of young families expecting their first baby were studied in maternity health care clinics. The first phase of the Finnish Family Competence Study included a total of 1414 fathers. Of these, 1279 responded to the questionnaire, the drop-out rate being 9.5%. Basic educational level, age, occupation and location of present and childhood home were used as demographic variables. Socio-economic factors of the father, his wife and his parents were also studied. The fathers were asked to give their own estimation of their smoking and alcohol consumption before and during the wife's pregnancy. Changes were seen in alcohol consumption, studied in relation to the amount consumed at one drinking time, frequency of alcohol consumption, age, and location of childhood home. Changes in smoking habits were studied in the same way. According to the fathers' own assessment, they reduced smoking and drinking of alcohol during their wives' pregnancies. Parents seem to transmit their own patterns of health behaviour to their children, and the model provided by them is highly important.