Udder conformation traits such as udder depth are favorably associated with somatic cell score (SCS) and mastitis resistance, but unfavorably associated with yield, resulting in unclear selection aims. Data envelopment analysis (DEA) is an approach to characterize the efficiency of different units based on inputs and outputs. The objective of this research was to use DEA to create an efficiency trait for udders of Brown Swiss cattle, which we termed udder efficiency, and to evaluate the genetic relationship of udder efficiency with yield, fitness, and udder conformation. The lone input was identified as milking speed and the outputs were milk, fat, and protein yield, and the inverse of SCS. A SAS DEA macro was used to determine udder efficiency relative to herdmates, with the most desirable cows milking quickly, producing large volumes of milk, fat, and protein with a low SCS. Values for the trait ranged from 0.03 (very inefficient cows) to 1.0 (efficient cows). There were 105,164 first through fifth lactation yield and SCS records from 45,464 cows born in 2000 or later. There were 41,704 milking speed records with a high score corresponding to faster milking speed. From these, 40,960 udder efficiency records were derived. These data were analyzed using a series of 3 trait models in ASREML that included fixed effects for lactation, age, and herd-calving cluster. Random effects were animal, permanent environment, and residual. The heritability of udder efficiency was 0.23 ± 0.0133. Genetic correlations with udder efficiency were moderate and positive for yield (0.40 to 0.42), favorable with SCS (−0.21), and strongly positive for milking speed (0.86). Udder efficiency was also strongly correlated with productive life (0.69). Of the udder traits, rear udder height (0.30), teat length (−0.28), fore udder attachment (0.25), and rear udder attachment (0.21) were most favorably correlated to udder efficiency. The correlation of udder depth with udder efficiency was 0.16. Based on these findings, DEA could be a useful and novel method for evaluating udder efficiency, helping to identify traits that enable selection for mastitis resistance without compromising yield.