Background Schengen Agreement grants easier international movements within Europe, and the still ongoing enlargement of Schengen Area (Romania, Croatia and Bulgaria will probably join it in the next few years) is expected to enhance migratory fluxes towards Italy. According to European Centre for Social Welfare Policy and Research, there is a “widespread lack of information about migrants’ health needs and access to services”, which is necessary to provide them better health care. It is known that both Italians and immigrants mainly suffer of chronic pathologies, but more specific data are poor in Italy. Therefore, the aim of the study is to analyse the epidemiology of chronic diseases (CD) in undocumented immigrants in the province of Pavia (Northern Italy), in which irregular immigration is a spreading phenomenon. Methods Data were collected from patients referring to STP (Strangers Temporarily Present) Clinic, which is managed by volunteer doctors and medical students, and provides free health care for irregular immigrants in Pavia province. According to WHO indications we classified CD in: hypertension, cardiovascular diseases, cancer, chronic respiratory diseases, diabetes and degenerative osteoarthropaties. Data are expressed as absolute number; OR [95%CI] and chi squared test were used for prevalence correlations. Results Complete data were available for 259 patients (156 women, 103 men), with mean age 46.4±16.9 years, visited for the first time at STP Clinic 2.9±1.7 years ago. Patients were Caucasians (164), Africans (75), Americans (14) and Asians (6). Total number of CD cases was 203. CD were diagnosed in 140 subjects, of whom: 95 (45.9% of patients with CD) affected by only 1 CD; 43 (36.7%) by 2-3 CD; 2 (0.8%) by 4 or more CD. Hypertension affects the largest group of patients: 61 (23.6% of all subjects), followed by: osteoarthropaties: 53 (20.5%); diabetes and cardiovascular diseases, each of them 26 (10.0%); cancer: 24 (9.3%); respiratory diseases: 13 (5.8%). Prevalence of CD is influenced by age: the probability of being affected in patients >65 years of age is significantly higher than in the group between 18 and 65 years: OR 2.62 [1.21-5.67; p=0.01]. Conclusion Chronic diseases prevalence in irregular immigrants (54.1%) is considerably higher than the epidemiologic expectancy among Italian population of the same area (36.9%). These results show that Pavia province Health System’s efforts should focus on prevention and follow-up of CD also – even more – in undocumented immigrants.