The Milanino is an Italian chicken breed included in a conservation project run by the University of Milan. It is characterized by good fertility, heavy body weights, high adaptation ability to adverse climate conditions, and disease resistance. Because of these characteristics, the Milanino could represent an important genetic resource for alternative production systems. This research was aimed at studying the effect of bird density on growth and slaughter performance, as well as stress response in Milanino chickens kept in outdoor pens. One hundred and sixty Milanino chickens were randomly assigned to 2 experimental groups kept at different densities (2 m2/bird and 8 m2/bird) and were slaughtered at 185 days of age. Growth and slaughter performance and stress condition were recorded. The interaction bird density * sex * age significantly affected body weight and an opposite trend was found between females and males: heavier females were found in the high-density group, while heavier males were found in the low-density group. Bird density did not affect carcass weight data. The stress marker (H/L ratio) was significantly higher in birds kept at the higher density (2 m2/bird). In conclusion, the Milanino provided satisfactory growth performance with different rearing density but the lower density, 8 m2/bird, should be preferred to minimize welfare problems for male birds.