One of the most important aim of public health is to provide an accurate evaluation of the population health conditions, its need for care and related costs.
Usually, the estimate of prevalence for the most common chronic conditions (CCs) is calculated using direct methods such as prevalence surveys  but also indirect methods using health administrative databases that collect this information for other reasons were used .
Ideally, prevalence surveys that estimate the prevalence of CCs by a clinical evaluation, and not only by self-reported information from subjects should be performed. However, they are expensive and when performed were limited to elderly and in specific geographical areas [3, 4].
Prevalence surveys based on self-reported information are regularly conducted in several countries to provide estimates for several CCs [1, 5]. Some of these surveys present the advantage to be not particularly expensive but, at the same time, they are criticized because the presence/absence of the disease is self-referred and thus conditioned by potential bias. Furthermore, these surveys refer to a sample of the population and thus are also limited by the sampling uncertainty. In particular, these estimates could be biased because some individuals likely might not be reached by the survey (e.g., very old people living in retirement homes).
As far as the use of health administrative databases to estimate the prevalence of some diseases, hospital discharge registries are those more often used because they collect specific information about diagnoses . However, in some cases the accuracy of diagnostic code can be low [7, 8]; furthermore, for some diseases the probability of being hospitalized, also for a long period, is very low and thus it might underestimate the actual prevalence.
The health administrative database of the general practitioners (GPs) has also been used to estimate prevalence given that for some conditions it is likely that a subject with the studied disease may be in charge of the GPs [9, 10]. However, GPs are not formally requested to collect specific databases with information about diseases and they collect data quite exclusively for facilitating their routine management such as drug prescriptions, doctor's notes, et cetera. This means that the quality about diagnosis may be heterogeneous; furthermore, for some CCs, GP has likely very few contacts with the patients; finally, at least for Italy, the access by public health services to GP's databases is impossible given that there are no statutory compliances for that.
Recently, the use of drug prescription database has been proposed to estimate the prevalence of specific CCs [11, 12]. This can be done when the drug prescriptions are unambiguously used for the treatment of these diseases (e.g., insulin for diabetes mellitus). In Italy drug prescriptions are collected at regional level and the coverage is expected to be extremely high because they are used for reimbursement by the regional health service (RHS).
The objective of this study is to provide estimates of prevalences of people diagnosed with several CCs in Lazio region, Italy, in 2006 using the drug prescription's database and to compare these estimates with those obtained using other health administrative databases. These prevalence estimates were also compared, when possible, with that reported by the survey performed in 2004-2005 by the Italian bureau of census (ISTAT) .