Abstract Purpose The KLIK Patient-Reported Outcome Measure (PROM) portal is an evidence-based intervention implemented in clinical practice in > 25 Dutch hospitals for patients (children and adults) who regularly visit the outpatient clinic. Implementation science frameworks can be used to understand why implementation succeeded or failed, to structure barriers and enablers, and to develop implementation strategies to overcome barriers. This paper aimed to (A) retrospectively describe determinants of successful KLIK PROM implementation using the Consolidated Framework for Implementation Research (CFIR), and (B) identify current barriers and match implementation strategies. Methods (A) The KLIK implementation process was described retrospectively based on literature and experience, using the 39 CFIR constructs organized in five general domains: intervention characteristics, outer setting, inner setting, characteristics of individuals, and implementation process. (B) The CFIR-Expert Recommendations for Implementing Change (ERIC) Implementation Strategy Matching tool identified current barriers in the KLIK implementation and matched implementation strategies that addressed the identified barriers. Results (A) The most prominent determinants of successful KLIK PROM implementation lie in the following CFIR domains: intervention characteristics (e.g., easy to use), characteristics of individuals (e.g., motivation), and process of implementation (e.g., support). (B) 13 CFIR constructs were identified as current barriers for implementing the KLIK PROM portal. The highest overall advised ERIC strategy for the specific KLIK barriers was to identify and prepare champions. Conclusion Using an implementation science framework, e.g., CFIR, is recommended for groups starting to use PROMs in clinical care as it offers a structured approach and provides insight into possible enablers and barriers.