Although social housing has been associated with improved welfare in farm animals, little is documented about the early life behavior or the disease dynamics of pair-housed calves. Our objective was to describe and analyze the behavior of pair-housed calves from day 1-10 of life, together with the disease dynamics within pairs during the first 30 days of life. An observational study was conducted in the summer of 2020, in a calf facility in Northern Colorado, USA. A total of 58 pairs of Holstein heifer calves were enrolled at birth and followed for 1 month to analyze disease dynamics within pairs housed together. A subgroup of 15 pairs of calves were video recorded to assess the dynamics in their behavior until 10 days of life. Calves were video recorded 3 times per day (AM, Noon, PM) for 60 min before and after each milk feeding (360 min/day). Behaviors of interest were resting and active time, play behavior, and time spent alone or together. Calf health was assessed 3 times per week. Linear mixed models were completed to evaluate differences in behavioral outcomes across days, considering pair as a cluster. Mean (SE) resting time ranged from 75.5 (2.8) to 107.9 (3.4) min per 120 min period, while active time ranged from 15.6 (6.9) to 84.5 (5.2) min per period. Calves modified their resting/ active time over the monitoring period in both the AM and PM periods. Notably, calves spent over 50% of the active time performing play behaviors. From day 2, calves increased their active time interacting in social or synchronized play behaviors. Moreover, calves increased their time together inside the hutch in the AM from 17.9 (8.7) to 46.7 (9.1) min. Similarly, they increased their time together outside the hutch in the AM from 7.3 (3.6) to 31.4 (3.6) min, and during the PM from 3.5 (4.9) to 27.4 (5.5) min. Regarding disease presentation, 98% of the calves had events of abnormal fecal consistency within 30 days of life. However, 26% of the pair mates did not develop disease within 5 days following the diagnosis of the initial case within the pair. Furthermore, 75.6% of the abnormal fecal consistency cases were moderate, and 71.4% of pen mates did not show the same level of severity. Young calves modified their behavior towards a more social setting, despite challenging environmental conditions associated with the summer season. Diarrhea did not develop in all pair mates regardless of contact.