• Relevant quality issues were raised in all assessment procedures. • Lack of efficacy and severe safety risks were decisive for non-approval. • Experimental characteristics of approved ATMPs urge stakeholders to guard patient risk. • Methodologies for development and regulation need to be continuously evaluated. A comparative analysis of assessment procedures for authorization of all European Union (EU) applications for advanced therapy medicinal products (ATMPs) shows that negative opinions were associated with a lack of clinical efficacy and identified severe safety risks. Unmet medical need was often considered in positive opinions and outweighed scientific uncertainties. Numerous quality issues illustrate the difficulties in this domain for ATMP development. Altogether, it suggests that setting appropriate standards for ATMP authorization in Europe, similar to elsewhere, is a learning experience. The experimental characteristics of authorized ATMPs urge regulators, industry, and clinical practice to pay accurate attention to post-marketing risk management to limit patient risk. Methodologies for ATMP development and regulatory evaluations need to be continuously evaluated for the field to flourish.