Summary Epidemiological evidence has generally supported a protective association of physical activity with large-bowel adenomas, but whether the protective effects are restricted to recent or past activity is uncertain. We determined whether recent and past recreational or total daily activity was associated with prevalence of colorectal adenomas among male and female members of a prepaid health plan in Los Angeles who underwent sigmoidoscopy (n = 488 matched pairs). Participants, aged 50-74 years, completed a 126-item semiquantitative food frequency questionnaire and were also interviewed regarding non-dietary risk factors in 1991-93. In the univariate analysis, all measures of recent recreational physical activity were associated with reduced prevalence of polyps. After adjustment for body mass index, smoking status, daily servings of fruit and vegetables, use of non-steroidal anti-inflammatory agents and intakes of calories, saturated fat and alcohol, the associations were weakened. For subjects engaging in high-intensity activities compared with subjects not engaging in vigorous activities, the multivariate odds ratio (OR) for recent recreational activity was 0.7 [95 % confidence interval (Cl) 0.4-1.1, trend P = 0.08]. Past recreational activity and past or recent total daily activity were not associated with prevalence of adenomas. These results support a modest association of recent recreational physical activity with prevalence of colorectal adenomas.Keywords: colorectal adenoma; physical activity; case-control study Results of epidemiological studies over the past two decades have fairly consistently supported a protective association of physical activity with cancer of the large bowel (Lee et al, 1991;Dosemeci et al, 1993;Fraser and Pearce, 1993;Potter et al, 1993;Longnecker et al, 1995). Because adenomatous polyps are likely precursors of colorectal carcinoma (Enterline et al 1962; Stryker et al, 1987;Jass, 1989;Pollock and Quirke, 1991), research has focused on risk factors for colorectal adenomas in recent years. Many studies have reported protective associations of physical activity with risk of colorectal adenomas (Kato et al, 1990;Kono et al, 1991;Benito et al, 1993;Giovannucci et al, 1996), and others have demonstrated more modest protective associations (Little et al, 1993;Giovannucci et al, 1995;Sandler et al, 1995). Whether the protective effects are greater among certain subgroups of the population or are restricted to recent or past activity is uncertain.In the present study, extensive data on diet, smoking and other lifestyle factors were collected and controlled in the analyses of several indicators of recent and past physical activity with colorectal adenomas among men and women who underwent sigmoidoscopy in Los Angeles. METHODSSubjects of either sex were eligible for the study if they underwent sigmoidoscopy at either of two southern California Kaiser Permanente Medical Centers (Bellflower and Sunset) from 1 January 1991 to 25 August 1993 and fulfilled the following criteria: age 50-74...