The purpose of this study was to map quantitative trait loci (QTL) affectinghealth traits in Swedish dairy cattle. A genome scan covering 17 chromosomes wasperformed. Ten grandsire families were used in a granddaughter design. Nine ofthe families belonged to the Swedish Red and White breed, which is related toother Nordic Ayrshire breeds, and one family was of the Swedish Holstein breed.A total of 417 bulls were genotyped for 116 microsatellite markers distributedover 17 chromosomes. Daughter yield deviations for clinical mastitis, somaticcell count (SCC), and other diseases (OD) were included in the analysis. Leastsquares interval mapping using putative QTL as cofactors was applied both withinand across grandsire families. Significance thresholds were set by permutationtests. In the across-family analysis, we detected 8 suggestive QTL and 3 QTLsignificant at the genome level. The QTL affecting clinical mastitis were foundon 3 chromosomes (9, 11, and 25), 4 QTL for SCC were found (on chromosomes 5, 9,11, and 23), and we detected 4 QTL for OD (on chromosomes 9, 11, 15, and 25). Inaddition, we found several QTL that segregated within single families but wherethe QTL effect was not significant in the across-family analysis. In conclusion,we were able to locate QTL for all 3 analyzed traits, and overlapping QTL forseveral traits were observed.