The objectives of this study were to measure lying behavior and social interactions oflactating cows housed in an alternative bedded pack system commonly referred to as a compost dairy barn, and to investigate the association between temperature-humidity index (THI) and lying behavior of these cows. Lying, standing and walking behavior of 147 focal cows on 12 dairy farms was measured using automatic activity monitors. Daily lying time was 9.34 ± 1.94 h. Number of daily lying bouts was 11.0 ± 3.2 and the lying bout length was 50.8 ± 35.6 min. Lying behavior had an inverse relationship with the THI during the monitoring period. Cows in the compost barns laid down for less time, took more steps, and reduced the length of lying bouts as the temperature-humidity index increased. Social interactions and lying positions of all cows in the bedded pack area (total of 886 cows on the 12 dairies) were recorded using visual observations during two 4-h periods on 2 separate days. All 4 natural lying positions (head back, head up, flat on side, and head on ground) were observed in 9 of the bedded packs during the direct visual observation periods. A majority (84.6%) of the cows observed lying down assumed the head-up position. Observations of social interactions on the bedded pack area showed that 0.94 ± 1.5 incidents of chasing away, 0.94 ± 1.8 of pushing, 1.4 ± 1.6 of head butting, and 2.3 ± 2.9 of allogrooming (social licking) occurred per hour. Observations of lying behavior, social interactions, and natural lying positions indicated that compost dairy barns can be an adequate housing system for dairy cows.