Waiting list parameters calculated for defined dates and time periods allow studies to determine balance between new and completed referrals. The authors discuss various sub-groupings of the waiting lists. The main waiting time parameter is mean waiting time for the various levels of care in the case of the different medical specialties and diagnostic groups. Waiting time is defined as the difference between date of first admission to hospital and the date when the patient was referred. It is possible to calculate total waiting time for patients undergoing out-patient evaluation before in-patient or day-care treatment. Aggregated waiting times should exclude control admissions and admissions postponed at the wish of the patient.