Background. The number of immunocompromised (IC) adults in the United States is likely increasing due to new indications for immunosuppressive treatments and to improvements in medical management and life-expectancy of these adults. Such increases can have major public health implications due to risks from reactivation of chronic infections (e.g. tuberculosis, toxoplasma, zoster) and from exposure to opportunistic infections (e.g. listeria, cryptosporidium). Yet comprehensive data on prevalence of all-cause IC have never been published. We report data on prevalence of self-reported IC adults in the United States.