Beginning in 1962, each French census has included a question that asks for a person's place of residence on 1 January of the year of the last census(1). However, if we want to measure temporal trends in internal migration in France, the information provided by this question cannot be used directly and in fact raises two problems that are hard to overcome.First, even if the period over which migrant numbers are measured is constant (for example an interval of five years, as in Australia, Canada, Great Britain, Japan and the United States, around the 1970s (Long and Boertlein, 1976)), an estimate has to be given of the annual average migration rate. Yet many studies have shown that because of repeat and return migration by the same individual, the number of migrants such a question measures is not even approximately equal to five times the annual number (Courgeau, 1973; Long, 1988; Rees, 1977). Without additional information, therefore, this migrant count measured over a period of five years cannot be used to estimate the corresponding annual number. The simple solution to this problem is to ask the same question for a period of one year, as has been done in Australia, Great Britain, Japan and the United States, in the same censuses (Long and Boertlein, 1976). It then becomes clear that the rate over five years is not five times higher than the annual rate. In the United States, for instance, for an annual rate of 19.2% the corresponding five-year rate is 47.0% as compared with an expected rate of 96.0%. Repeat and return migration is responsible for this two-fold difference.Second, unlike other countries where this question is asked over a period of five years prior to the census, allowing measurement over a constant period between successive censuses, estimation of annual rates of migration is made even harder in France by the large variation in the periodicity of the census (ranging between six and nine years).These two problems must be addressed by analysing the successive moves made by individuals, based on finely detailed survey data, and by modelling this distribution over time using a small number of parameters.1. Short presentation of the model and the evaluation of its parametersWe demonstrated (Courgeau, 1973) that this was possible and that the model applied to migration in such diverse contexts as the United States (Morrison, 1970), Sweden (Wendel, 1953) and France (for which the estimation was made using an INED Demographic Situation survey, presented in Girard and Zucker, 1968). It should be noted, however, that although the model for these three countries is the same, the parameter estimates differ greatly. For any one country, these parameters will also vary over time. In what follows we present a new estimation of their value based on the Labour Force Surveys from 1991 to 1999 and the Young People and Careers survey of 1997 (L'Hospital, 2001) and we apply these new parameters to data from the 1999 census.Longitudinal and period analysis of data for France and for the United States and Sweden lead to the following conclusions:1) The probability for a person who has migrated once of migrating again in the future, K, is largely independent of the previous migration's rank order but is affected by the geographical subdivision on which moves are measured.2) For the population that will migrate again in the future, the annual hazard rate for this migration is independent of the duration of residence between each migration, the rank order of this migration and the geographical subdivision used. The instantaneous hazard rate of a new migration, k, has of course the same properties.3) Return migration to an area of origin is proportional, in the ratio /, to moves of a rank higher than one, made throughout the period under study. It follows that the probability for a person who has migrated of making a return migration is Kl.We have merely to estimate using existing data a probability of nonmigration corrected for return migration(2) K(1 + l) and the instantaneous hazard rate for a new migration k, in order to get from a number of migrants M(t) to a number of migrations Ppi made in the same period, and hence to an instantaneous hazard rate of migration. …