The West of Scotland has traditionally been a focus for Irish migration. Using data from two studies carried out in this region, one quantitative, the other qualitative, this paper shows little difference in drinking and smoking between Scots of Irish descent and other Scots. It does, however, show significant differences in these behaviours according to religious affiliation in adulthood. Rather than confirming the stereotype of Irish Catholics as heavy drinkers and smokers the present paper puts forward the hypothesis that drinkers and smokers are differentially retained in membership by different religious affiliations, and argues that this accounts for differences in reputation and in health-related behaviours.