A divergent selection experiment on mastitis resistance of Holstein and Normande cows was carried out at Le Pin, the INRA experimental farm. Two lines, one resistant to mastitis and one control, were produced by using bulls with contrasted breeding values for a combination of somatic cell score (SCS) and clinical mastitis (CM). In Holstein, the same population was also split into two groups diverging for body condition score (BCS) and obtained by selecting the sires on their BCS breeding values. This paper presents the first results on the observed differences between lines based on data of 268 cows. Overall differences in SCS, CM, infectious status (assessed by bacteriological PCR tests) and BCS were in agreement with genomic predictions. Within-breed differences were similar, but sometimes not significant for udder health traits. These cows support extensive phenotyping for explanatory traits to explain the biological pathways involved in these differences.