Using the Monte Carlo simulation tool GEANT4, we simulated the hadron-therapy beam line of the Centro di AdroTerapia ed Applicazioni Nucleari Avanzate (CATANA) center. This is the unique Italian hadron-therapy facility in which 62-MeV proton beams are used for the radiotherapeutic treatment of choroidal and iris melanomas. All the elements, such as diffusers, range shifters, collimators, and detectors, typical of a proton-therapy line were modeled. The beam line provides an ideal environment for the experimental testing and validation of the software developed. The software architecture was developed, and the validation of the software is in its final stage. Simulated ranges, energy distribution, depth and lateral dose distributions for full energy proton beams will be compared to the experimental results obtained at La boratori Nazionali del Sud (LNS) with different detectors. © 2005 IEEE.