Data was collected on temperature and humidity profiles throughout the growth cycle, management practices and equipment that contributed toe variation in environmental conditions and how bird welfare was affected by environmental variables for different stocking densities (30, 34, 38, 42, and 46 kg/m2. Broiler health and welfare varied the most when the house temperature and relative humidity was maintained within limits recommended by the breeder company. During the first week of life, relative humidity was found to be very important for later health. This suggests that welfare may improve if there is better control of humidity. Welfare was also influenced by ventilation and air control, type of drinker, numbers of stockpersons and litter type. In summary, controlling environmental variables, such as temperature, humidity, air and litter quality, is very important for ensuring broiler welfare. Stocking density is also important, but the environmental variables also have to be considered if stocking density is lowered. To maximize bird welfare, standards need to be set for stocking density, environmental variables, and the genetic makeup of the birds.