Successively slaughtered poultry flocks were sampled for Salmonella to study the relationship between gastrointestinal colonization of the birds and contamination of the carcasses after slaughter. Samples from 56 broiler flocks and 16 spent layer and breeder flocks were collected in six slaughterhouses. Salmonella isolates were serotyped and further characterized by pulsed-field gel electrophoresis (PFGE). Although only 7 (13%) broiler flocks were colonized with Salmonella at slaughter, carcasses of 31 (55%) broiler flocks were contaminated after slaughter. Concerning the layer and breeder flocks, 11 (69%) flocks were colonized in the gastrointestinal tract, but after slaughter, carcasses of all flocks were contaminated. The Salmonella status determined at the farm did not always correlate to the status at slaughter. On the other hand, the slaughter of Salmonella-colonized flocks did not always result in the contamination of the carcasses with the same PFGE types isolated from the gastrointestinal tract. When only uncolonized flocks were slaughtered, the carcasses of flocks were on some occasions still contaminated with Salmonella. This indicates possible cross-contamination from the slaughter equipment or transport crates. These observations show that it is difficult to reach the benefits of logistic slaughter in commercial poultry slaughterhouses.