While many participate in kink and BDSM activities, even lifestyles as part of a community or for exhibitionism, estimates and polls place those involved in power exchange relationships and kink practices to be far greater than those who live a public lifestyle as part of BDSM culture, though they may not necessarily identify as such consciously.
A study of 20,000 Australians by public health researchers at the University of New South Wales found that 2% of adult Australians regularly partake in sadomasochism and dominance and submission-type sexual role play.
In a representative study published in 1999 by the German Institut für rationale Psychologie, about two thirds of the interviewed women stated a desire to be at the mercy of their sexual partners from time to time. 69% admitted to fantasies dealing with sexual submissiveness, 42% stated interest in explicit BDSM techniques, 25% in bondage.
A 1976 study in the general US population suggests three percent have had positive experiences with Bondage or master-slave role playing. Overall 12% of the interviewed females and 18% of the males were willing to try it.
A 1990 Kinsey Institute report stated that 5% to 10% of Americans occasionally engage in sexual activities related to BDSM. 11% of men and 17% of women reported trying bondage (Ernulf, K. E., & Innala, S. M. (1995). Sexual bondage: a review and unobtrusive investagation. Archives of Sexual Behavior, 24(6).)
According to a 2005 survey of 317,000 people in 41 countries, about 20% of the surveyed people have at least once used masks, blindfolds or other bondage utilities, and 5% explicitly connected themselves with BDSM. In 2004, 19% mentioned spanking as one of their practices and 22% confirmed the use of blindfolds and/or handcuffs.
From sampling this information we can see that a tiny minority of populations engages in BDSM as a lifestyle (i.e. they incorporate it into the majority, if not all, of their sexual experiences and it is considered a vital piece of their sexuality); yet a much larger portion of the populations are interested in or occasionally incorporate BDSM it into their sex life, but it isn't a crucial part of it.
Of those who knowingly practice BDSM as a lifestyle, estimates from private online polls place 2/3's to do so privately without ever discussing it in public or with friends.
See also Coming Out.