Background: Chronic ankle instability (CAI) is a multifactorial disabling condition. Ideally all factors contributing to CAI are identified and implemented in a risk assessment model. However, they need to meet strict reliability requirements. To assess usability of radiographic factors for this risk assessment model and future clinical practice, the objective of the current study was to assess the intra and inter observer reliability of three radiographic measurements. Methods and methods: The radiographs of 39 consecutive patients, at least 16 years, who visited the Emergency Department after sustaining a LAS, were assessed by four observers. The radiographic measurements included absolute and relative ankle alignment, sagittal fibular position and ankle joint congruency (talar radius and height, and tibiotalar sector), performed twice by all observers independently. Reliability was assessed by calculating the Intraclass Correlation Coefficient (ICC) which was considered good when ICC > 0.70. Results: The intra observer reliability of the absolute and relative fibular position, and talar height were good to excellent, (ICC 0.84–0.98, 0.85–0.98, and 0.79–0.93, respectively). The talar radius (ICC 0.69–0.89) was moderate to good. The overall inter observer reliability was good for the absolute and relative fibular position, and talar radius (ICC 0.84, 0.86, and 0.79, respectively). Other measurements had ICC values of <0.70. Conclusions: In an effort to identify the multifactorial nature of CAI, both the fibular position and the talar radius measurements showed good observer reliability, and will be implemented in a future risk assessment model. The other measurements are too prone for measurement errors, for future reference. Level of evidence: IV Case Series.