Constipation is a common heterogeneous condition, possibly encompassing different clinical subtypes. Little is known about the comparative epidemiology of constipation subtypes. This study was conducted to estimate the prevalence of constipation subtypes and determine whether subtypes differ by sociodemographic factors. Between June and September 1997, a telephone interview was conducted with individuals about their bowel habits in the preceding 3 months. Survey data on 15 constipation-related symptoms were used to identify individuals who met prespecified symptom criteria for the following mutually exclusive subgroups: functional constipation, irritable bowel syndrome (IBS), outlet obstruction or delay (outlet), both IBS and outlet (IBS-outlet), and frequent laxative users (i.e., at least every other day). A total of 10,018 eligible individuals in the United States 18 yr of age or older completed the interview. Test-retest reliability of reporting symptoms was assessed in a separate national survey. The Spearman's correlation coefficient for reporting symptoms ranged from 0.54 to 0.83; all but three symptoms had correlations above 0.68. The overall prevalence of constipation was 14.7%. By subtype, prevalence was 4.6% for functional, 2.1% for IBS, 4.6% for outlet, and 3.4% for IBS-outlet. An additional 1.8% of respondents reported laxative use at least every other day. Outlet was the most common subtype among women, whereas functional constipation was the most common subtype among men. The gender ratio varied by subtype, with elevated ratios for outlet (F/M = 1.65) and IBS-outlet (F/M = 2.27) subtypes. The age pattern differed among each of the four subtypes. Prevalence of functional subtype decreased with increasing age. In contrast, outlet subtype did not seem to vary by age, and IBS (both men and women) and IBS-outlet (women only) subtypes increased to age 35 yr and declined thereafter. Prevalence of functional constipation increased with increasing education. Outlet type was more common in nonwhites compared to whites. Finally, 45% of individuals with constipation reported having the condition for 5 yr or more. Constipation is a heterogeneous condition. Differences in epidemiological profile by age, sex ratio, and relation to other sociodemographical factors support the distinction of two and possibly more symptom-based subtypes.