The effect of bad sanitary conditions on growth performance and feeding behaviour were studied on a total of 48 Large White pigs between 95 and 130 d of age. This experiment carried out during the hot season in a tropical humid climate. Two groups of 12 pigs each were housed in a clean environment in which the pens were disinfected thoroughly prior to stocking and maintained in a clean state by daily washing the pens and by weekly emptying the manure stored beneath the partial concrete floor. The dirty environment was achieved by not cleaning the pens prior to stocking or throughout the experiment and by storing the manure beneath the floor slats throughout the experimental period. The microbial pressure was increased by introducing 5 additional non experimental pigs near each experimental dirty pen. Feeding behaviour parameters were measured using automatic feed dispensers. Pigs housed in a clean environment consumed more feed (2.283 vs. 1.953 kg/d; P < 0.001) and grew faster (871 vs. 780 g/d; P < 0.05) than those housed in the dirty environment. No significant effect on treatment was reported for the feed conversion efficiency (2.70 kg/kg on average). The reduced average daily feed intake in dirty pens was associated with a reduction of the meal size (334 vs. 282 g/meal; P = 0.10) whereas the meal frequency was not affected by treatment (7.5 meals/d on average). The rate of feed intake was significantly higher in the clean than in the dirty environment (34.0 vs. 29.9 g/min; P < 0.05).