For many species several similar QTL mapping populations have been produced andanalyzed independently. Joint analysis of such data could be used to increasepower to detect QTL and evaluate population differences. In this study, datawere collated on almost 3000 pigs from seven different F(2) crosses betweenWestern commercial breeds and either the European wild boar or the ChineseMeishan breed. Genotypes were available for 31 markers on chromosome 4 (onaverage 8.3 markers per population). Data from three traits common to allpopulations (birth weight, mean backfat depth at slaughter or end of test, andgrowth rate from birth to slaughter or end of test) were analyzed for individualpopulations and jointly. A QTL influencing birth weight was detected in oneindividual population and in the combined data, with no significant interactionof the QTL effect with population. A QTL affecting backfat that had asignificantly greater effect in wild boar than in Meishan crosses was detected.Some evidence for a QTL affecting growth rate was detected in all populations,with no significant differences between populations. This study is the largestF(2) QTL analysis achieved in a livestock species and demonstrates the potentialof joint analysis.