In a study of 5,571 patients from the general surgery departments of 11Israeli hospitals, the crude overall wound infection rates showedinterhospital heterogeneity. The rates ranged from 6.3% to 12.4% (P(X2) = 0.039). Controllingfor the different distributions of procedures performed in the variousinstitutions did not reduce this variability. None of the hospitals hadeither consistently high or consistently low infection rates. A hospitalcould have low rates for one procedure and high rates for another.Therefore, the decision was made to proceed with procedure-specificanalyses. This article details results of the analysis of 1,487 herniaoperations. Four variables (old age, infection at another site,incarceration, and introduction of drains) accounted for almost all thedifferences in infection rates among the institutions. Of the four, presenceof drains had the strongest association with infection (P derived from thelogistic model <0.001). The risk was consistent in all hospitals and wasunconfounded by other measurable factors. In contrast, the pattern of usingdrains seemed arbitrary and inconsistent, ranging from 9% of patients in onehospital to 41% in another. These findings were used as a basis fordiscussion with the surgical teams and for the initiation of a randomizedclinical trial on the use of drains in hernia operations.