Background <p>Medical residents are among the most vulnerable healthcare workers making their job satisfaction a critical factor influencing mental health, quality of care, and retention. This study examines how resilience and perfectionism are associated with job satisfaction among Croatian medical residents, with particular attention to perfectionism’s mediating role in these relationships.</p> Methods <p>In a cross-sectional study, 148 residents (79.1% female; median age 30 years, IQR 29–32) completed an online survey between April and May 2024. Snowball sampling was conducted via closed social media groups for residents. Instruments included validated Croatian versions of the Brief Resilience Scale, the Multidimensional Perfectionism Scale, and the Index of Job Satisfaction.</p> Results <p>Participants were most frequently in their third year of training (Md = 3, IQR = 2–4); the most common specialty was anesthesiology (<i>n</i> = 17). Concern about mistakes, a maladaptive dimension of perfectionism, was negatively correlated with resilience (<i>r</i> = -0.476, <i>p</i> &lt; 0.001) and job satisfaction (<i>r</i> = -0.375, <i>p</i> &lt; 0.001). Regression analysis identified concern about mistakes as the sole predictor of job satisfaction (adjusted <i>R</i>² = 0.112). Mediation analysis showed that concern about mistakes partially mediated the relationship between resilience and job satisfaction. Other perfectionism dimensions were not significant predictors.</p> Conclusions <p>This study found that concern about mistakes, a maladaptive form of perfectionism, mediated the relationship between resilience and job satisfaction among Croatian medical residents. Other perfectionism dimensions were not significant predictors. These findings highlight maladaptive perfectionism as a key factor influencing resident resilience and job satisfaction.</p>