The results of two questionnaire surveys of migrant owner-occupiers in Northampton, England, are reported. The major focus of interest is the importance of changes in the family life cycle in promoting mobility as a consequence of changing housing needs. It is demonstrated that demographic changes did not necessarily predispose households to move to acquire more space. Households which moved because of increased pressure on their housing space were significantly less well provided with space, but they had not experienced greater demographic change. They had always been relatively less well provided. It is suggested that this is because they opted to substitute either a newer or a more detached house for more space when they purchased the property. The behavioural model of residential mobility is reassessed in the light of these findings.