Like most agricultural production systems, effective decision making in turkey production systems requires the prediction of future status of the system and evaluation of alternative management policies. A simulation model of a turkey production system was developed to predict values of flock performance indicators of significant economic importance, namely body weight and feed consumption. Existing weather simulation models were combined and modified in order to develop a model that predicted daily dry-bulb temperature and humidity ratio outside the turkey house. The weather simulation model was validated using twenty years of daily observed weather data from Roanoke, Virginia. Thermal environment inside the turkey house was predicted from simulated outdoor weather using energy and mass balance equations. House environment prediction part of the model was validated using observed inside and outside temperature data collected at a turkey farm in Virginia. A discrete event simulation model was developed to simulate the effects of house thermal environment, feed energy, sex, and age on weight gain and feed consumption of growing turkeys. The model was validated using temperature, body weight, and feed consumption data collected at a turkey farm in Virginia. The observed average bird weights at marketing age were within 95% confidence intervals of the predicted values. However, the model underpredicted energy consumption values. The sensitivity of the model to variations in R-value, ventilation rate, and feed energy concentration was evaluated. The model was more sensitive to feed energy concentration.