We identified the prevalence of adults who met the 1993 Centers for Disease Control and Prevention and the American College of Sports Medicine moderate physical activity recommendation and the 1996 Surgeon General's Report on Physical Activity and Health energy expenditure guideline for leading a moderately active lifestyle. Participants were 16,890 women and 12,272 men at least 18 years old who were asked in the 1990 National Health Interview Survey about their leisure-time physical activities. About one third of US adults met either recommendation for moderate activity; 32% met the Centers for Disease Control and Prevention and the American Association of Sports Medicine recommendation and 38% met the surgeon general's guideline. Women, ethnic minorities, adults with lower educational attainment, and older adults were least active. Public health efforts are needed to address the issues related to physical inactivity and to provide organized programs to increase moderate physical activity levels in US adults.