More Americans try to change their health behaviors through self-help than through all other forms of professionally designed programs. Mutual support groups, involving little or no cost to participants, have a powerful effect on mental and physical health, yet little is known about patterns of support group participation in health care. What kinds of illness experiences prompt patients to seek each other's company? In an effort to observe social comparison processes with real-world relevance, support group participation was measured for 20 disease categories in 4 metropolitan areas (New York, Chicago, Los Angeles, and Dallas) and on 2 on-line forums. Support seeking was highest for diseases viewed as stigmatizing (e.g., AIDS, alcoholism, breast and prostate cancer) and was lowest for less embarrassing but equally devastating disorders, such as heart disease. The authors discuss implications for social comparison theory and its applications in health care.