A grading system of anal incontinence (AI) is described that takes into account both degree and frequency of symptoms. A, B, and C indicate AI for flatus/mucus, liquid stool, and solid stool, respectively; 1, 2, and 3 indicate occasional, weekly, and daily AI. A scoring system, ranging from 0 (continence) to 6 (severe AI, i.e., daily AI for solid stool or C3) also is reported. Three hundred thirty-five patients have been evaluated by this method in our institution: 30 percent had severe AI, graded as C3; only 9 percent had mild symptoms graded as A. Both males and females could not control diarrhea (Grade B) in 44 percent of cases. Nearly half of the 110 patients who underwent surgery had a C3 incontinence before treatment. Positive results were achieved in 75 percent of cases after surgery: e.g., AI score significantly improved from 4.2 +/- 1.6 to 1.5 +/- 1.9 (P less than 0.001) in those with AI and rectal prolapse. Most of the failures were the patients with idiopathic C3 incontinence. In conclusion, this grading and scoring system allowed a satisfactory assessment of patients' AI before and after treatment. It may also be used to achieve an objective comparison between different series.