An F2 chicken population of 442 individuals from 30 families, obtained bycrossing a broiler line with a layer line, was used for detecting and mappingQuantitative Trait Loci (QTL) affecting abdominal fat weight, skin fat weightand fat distribution. Within-family regression analyses using 102 microsatellitemarkers in 27 linkage groups were carried out with genome-wide significancethresholds. The QTL for abdominal fat weight were found on chromosomes 3, 7, 15and 28; abdominal fat weight adjusted for carcass weight on chromosomes 1, 5, 7and 28; skin and subcutaneous fat on chromosomes 3, 7 and 13; skin fat weightadjusted for carcass weight on chromosomes 3 and 28; and skin fat weightadjusted for abdominal fat weight on chromosomes 5, 7 and 15. Interactions ofthe QTL with sex or family were unimportant and, for each trait, there was noevidence for imprinting or of multiple QTL on any chromosome. Significantdominance effects were obtained for all but one of the significant locations forQTL affecting the weight of abdominal fat, none for skin fat and one of thethree QTL affecting fat distribution. The magnitude of each QTL ranged from 3.0to 5.2% of the residual phenotypic variation or 0.2-0.8 phenotypic standarddeviations. The largest additive QTL (on chromosome 7) accounted for more than20% of the mean weight of abdominal fat. Significant positive and negative QTLwere identified from both lines.