The aim of the study was to determine the effect of increased stocking density on the microclimate of the outdoor group hutch, the health and growth of calves during the milk feeding period. Monitoring was carried out in one farm with 36 calf-bulls placed immediately after birth in individual outdoor hutches. At the age of 31 days, 16 calf-bulls were moved into group hutches of four with a housing area of 2.9 m2 per calf (control group), and 20 calf-bulls of five with a housing area of 2.3 m2 per calf (experimental group). Nutrition, water intake and bedding were the same for both groups of calf-bulls. Monitored indicators of microclimate (air temperature and relative humidity), health (occurrence of diarrhoeal and respiratory diseases) and growth of calves (live weight, weight gain) were evaluated in the TIBCO Statistics. The results show that an increasing of stocking density led to a deterioration of the microclimate in the outdoor group hutch. The calf-bulls reared in a group hutch of five had a non-significantly lower live weight at weaning at 60 days (by -2.2 kg) and lower weight gain (by -0.6 kg) compared to calf-bulls housed by four. The frequency of occurrence of respiratory diseases was insignificantly higher (+10.0%) in calf-bulls housed in an outdoor group hutch of five.