We study the impact that lower complexity in bank securitisations has on mortgage quality and the securitisation structure. We find that mortgages issued after the announcement of new European regulation that aims to reduce deal complexity are characterised by up to 0.38% lower annual delinquency rates than in the pre-regulation period. Similarly, we show that mortgage securitisations that meet the new ‘simplicity, transparency and standardisation’ (STS) criteria have 0.77% lower annual delinquency rates and are more resilient to adverse macro-economic shocks. We find that the increased quality of the underlying loans outweighs the potential negative effects of thinner subordinated tranches in securitisations that comply with the new regulation. Overall, our findings suggest that the new European securitisation regulation has contributed to improving credit quality in the securitisation market in Europe.