Most studies use quantitative measures to assess spatial planning outcomes. Instead, this paper proposes a novel qualitative framework to assess spatial planning outcomes that seek to understand why outcomes conform to, or deviate from, the intentions of spatial planning instruments. This novel framework links the conformance perspective with governance research. We tested our analytical framework in six Swiss and German municipalities. Drawing on interviews, observations and planning documents, our findings demonstrate which factors decisively influence planning outcomes. Our findings also demonstrate that high conformance does not necessarily equal spatial planning success. Qualitatively assessing planning outcomes contributes to the evaluation of the success and failure of spatial planning, and improves the implementation of planning instruments and practices accordingly.