Nonclinical safety investigations follow a strictly regulated, globally harmonized process and are essential for identifying potential adverse effects, thereby ensuring the safe use of new drugs. They are typically conducted in compliance with Good Laboratory Practice (GLP) quality standards and are required by regulatory authorities. For praziquantel (PZQ), a safe profile was consistently demonstrated in nonclinical safety pharmacology, general toxicology, genotoxicity, carcinogenicity, as well as developmental and reproductive toxicity studies. Although bioanalytical methods to establish exposure relationships and GLP quality standards were not established in the 1970s, the objectives, study designs, and key parameters investigated in in vivo studies largely resembled today’s requirements. In conclusion, PZQ has demonstrated a notably favorable safety profile in nonclinical investigations, which was confirmed by its safe use following market approval.