ABSTRACT. According to Swedish register data, regional size and the extent of commuting have both increased rapidly in recent decades. From the perspective of policy-making authorities, this would indicate good prospects for regional development, as small regions could be integrated into larger ones resulting in increased economic growth. However, there are few concrete manifestations of such regional enlargement, and alternative datasets give other impressions of the effects of commuting. Here we argue that this apparent growth might stem from several problems inherent in a register-based way of measuring changes in commuting patterns. Thus, regional enlargement and the extent of commuting may be exaggerated when measured conventionally, and the high hopes of using such enlargement to lever regional development might be misplaced. More generally, this study considers the problems arising as census or other enquiry and interview based data are replaced by register data.