Background: This study analyzes data related to Hospital (HOS), Public Treatment Service Dedicated to Drug Addicts (SERD), or Community Mental Health Center (CMHC) clients with a first diagnosis of Pathological Gambling (PG) in the period 2000/2016 in Northern Italy. The aims were to describe trends and characteristics of pathological gamblers (PGs) and to estimate the prevalence of other diagnoses before or after the diagnosis of PG. Methods: Participants aged over 17 years with an ICD-9 or ICD-10 PG diagnosis were selected. Results: 680 PGs were identified, mean age 47.4 years, 20% female, 13% non-natives, 30% had other mental disorders diagnoses, 9% had alcohol dependence syndrome, and 11% had drug dependence. Most participants with comorbid disorders were diagnosed before PG, with a more elevated prevalence regarding mental disorders. Almost seven years had elapsed on average between the first admission and the diagnosis of PG. Conclusions: The results of this study highlight a growing demand for PG treatment addressed not only to SERD, but also to psychiatric and hospital services, based on the increase in SERD attendance from 2013. Many of them had already been treated for mental health problems before, but their percentage remained costant over time.