The aim of this study was to determine how frequently pruritus ani (PA) is a symptom secondary to benign or malignant colon and anorectal pathology.One hundred nine patients with PA as the only presenting symptom were prospectively evaluated over a two-year period. All patients underwent anoscopy, rigid proctoscopy, and colonoscopy and were treated for PA. Patient data were entered into a computer data base and analyzed.The mean age was 52.1 years; males outnumbered females 2:1. The mean duration of symptoms was 6.1 weeks. Mean coffee intake was four cups per day. Forty-five percent of patients smoked and 45 percent drank alcohol daily. Thirty-five percent had an abnormal proctosigmoidoscopy or colonoscopy. Twenty-seven (25 percent) patients had primary pruritus and 82 (75 percent) patients had coexisting colon or anorectal pathology. The PA-associated neoplasia included rectal cancer (11 percent), anal cancer (6 percent), adenomatous polyps (4 percent), and colon cancer (2 percent). Hemorrhoids (20 percent) and anal fissures (12 percent) were the most common pruritus-related anorectal diseases. Among the 23 percent of patients with PA and neoplasia, pruritic symptoms were present longer compared with those with PA and anorectal disease < 0.001 and primary pruritus (P < 0.0001). All patients with primary PA were initially treated with dietary fibers, steroid cream, and drying agents. The recurrence rate for primary pruritus was twice that for anorectal disease (P < 0.0001).PA responds to treatment in 89 percent of patients, while 11 percent are refractory to treatment. Symptoms suggestive of pruritus ani, especially those of long duration, should alert the surgeon to the potential for proximal colon and anorectal neoplasia.