A total of 30,190 first-parity Danish Holstein cows housed in free stalls or tie stalls were analyzed to quantify to what degree genotype by housing interaction existed for 21 conformation and 2 workability traits. Each trait measured in different housing systems was treated as 2 separate traits in a bivariate animal model. Genetic correlations between the 2 traits as well as differences in genetic and residual variance were used as measurements of whether or not genotype by housing interaction occurred. Genetic correlations were in general close to unity (>0.9), except for body width (0.87 +/- 0.06). Genetic variance was greater (22% on average) for all traits except 2, whereas residual variance was greater for feet and leg traits and lower for body and udder traits when measured in tie-stall environments for nearly all traits. In total, this led to a greater heritability for traits measured in tie-stall barns. Conformation and workability traits measured in free stalls and tie stalls should not be considered as different traits when predicting breeding values, but heterogeneous variance could be accounted for.