Informal payments are deeply ingrained in the health care sector of most central, eastern and southern european countries. Evidence suggests that the price paid informally to medical staff is negotiated either directly or indirectly between patients and medical staff. The aim of this paper is to measure the imperfect information that exists on the amount that has to be paid informally to medical staff. We measure the extent to which patients pay more than the amount medical staff expect informally and the extent to which medical staff request less than patients are willing to pay informally. A two-tiered stochastic frontier model is developed to estimate indicators of patients’ and medical staff’s imperfect information on informal payments ...