An environmental risk assessment for losses to wastewater from galenical manufacturing of solid medicinal products at F. Hoffmann-La Roche in Basle, Switzerland, was performed based on an annual total materials balance. This balance resulted in a loss factor of 0.2% relative to the sum of all starting materials, which was later confirmed as valid by analysis for 1 specific active pharmaceutical ingredient (API). The initial risk assessment for all 25 different APIs formulated resulted in no evident risk for the wastewater treatment plant, based on biodegradation no-effect data. However, based on acute ecotoxicity data, potential risk to the local receiving water, the River Rhine, was identified from 1 single API, the antibiotic sulfamethoxazole (SMX). A refinement of the risk assessment for SMX, based on chronic ecotoxicity data, or the predicted no-effect concentration (PNEC), and documented sewage works degradability, or the predicted environmental concentration (PEC), led to a significant decrease of the initial PEC/PNEC ratio to well below 1. In view of this refinement, the final conclusion is that the galenical production investigated poses no significant risk to the environment.