Historical meat inspection data and production performance data collected from a large poultry processing plant in Norway were used to study the association between Clostridium perfringens infection and production performance in commercial broiler flocks. The study period was limited to the first 2.5 years after withdrawal of the in-feed antibiotic avoparcin, when necrotic enteritis was frequently seen. High levels of C. perfringens-associated hepatitis at slaughter were used as an indicator of C.perfringens infection. The contribution margins were 25 to 43% lower from flocks with high levels of C. perfringens-associated hepatitis than those with low levels. Impaired feed conversion ratio and reduced bodyweight at slaughter were major causes of the losses, while condemnations per se contributed to one-fifth of the losses in profit. Incidence of liver lesions showed remarkable variation throughout the study period, and there was considerable difference in frequency of liver lesions between farms.