A medication error (ME) is a drug-related problem that has been recognized as a common and serious threat to patient safety. The aim of this study was to detect and analyze ME reports occurring throughout the therapeutic process through the community’s pharmacies in order to improve the efficacy and safety of medications and contribute to the prevention of future MEs. This was a three-year descriptive, observational, and prospective study to detect and analyze the different MEs reported by the Catalan sentinel pharmacies network (Catalan SePhaNet). In total, 1394 notifications of MEs were reported (an incidence rate of 737.34 cases/100,000 inhabitants). MEs were detected more frequently in primary care centers. Most of the MEs reported were caused by an incorrect, incomplete, illegible, or verbal medical prescription (41.3%). Of the global notifications detected, 71.9% did not reach the patient (categories A and B). The drugs most frequently implicated in the reported ME cases were beta-lactam antibiotics. In 6.0% of the cases, the ME caused injury to the patient (categories E and F). In 72.0% of the global notifications, a pharmacist’s intervention avoided the ME. The importance of a community pharmacy and the role of a pharmacist were demonstrated in aspects related to patient and drug safety.