Objective: The capacity of healthcare professionals to tolerate uncertainty is of increasing research interest since it may reduce anxiety associated with managing complex health problems. Psychologists experience a high degree of uncertainty in their role. This longitudinal study examines changes in tolerance of uncertainty and confidence in case formulation among provisional psychologists as they progress through the early stages of training. Methods: Participants were 88 trainee psychologists from three postgraduate programs who completed surveys over three time points. In addition to measures of tolerance of uncertainty and confidence in case formulation the surveys included exposure to an ambiguous client vignette followed by a measure of state anxiety. Results: Repeated measures analysis of variance indicated significant increases in confidence in case formulation and confidence in response to the vignette over time. Hierarchical multiple regression indicated that state anxiety at time 2 was predicted by changes in tolerance of uncertainty in client care when time 1 state anxiety was controlled. The final model accounted for 31.2% of variance in participants responses. Conclusion: There is a need to better understand the educational and training activities that facilitate changes in confidence and uncertainty tolerance so they might be more effectively integrated into training programs. KEY POINTS: What is already known about this topic: As with healthcare fields more broadly, working as a psychologist involves a high degree of uncertainty. Postgraduate psychology curriculum does not include tolerance or management of uncertainty as a specific learning competency however indirectly provides strategies that promote uncertainty tolerance. Studies on medical trainees have reported that managing uncertainty becomes easier over time. No studies have examined changes in trainee psychologist’s ability to tolerate uncertainty as they progress through their training. What this topic adds: Confidence in case formulation increases over the early stages of postgraduate psychology training. Participant’s anxiety when responding to an ambiguous vignette at time two was predicted by changes in tolerance of uncertainty in client care, even when time one state anxiety was controlled. There is a need to better understand the educational and training activities that facilitate uncertainty tolerance and confidence in case formulation, so they might be more effectively integrated into training programmes.