Objective: Steroid-sensitive nephrotic syndrome (SSNS)in children is often complicated by one or more relapses, as manifested by the appearance of proteinuria. Besides health-related triggers, psychological stress might be related to relapse. This longitudinal study examined the link between perceived stress, emotional valence (feeling happy vs. unhappy)and daily reported proteinuria, and investigated the temporal relation between stressful events and proteinuria. Method: Sixteen children (4–13 years)diagnosed with SSNS were included. Patients kept an online diary for an average of 124 days, wherein they reported proteinuria (n = 1985 urine samples), perceived stress, emotional valence, medication use and health complaints. Stressful days were determined at the start of the study. Using multilevel analysis, the following associations were tested: (1)the relation between perceived stress, emotional valence and proteinuria, and (2)the temporal relation between stressful days and proteinuria. Results: Appearance of proteinuria was reported in 410/1985 urine samples. Perceived stress and not emotional valence significantly predicted proteinuria (95% CI [0.11, 0.27]), even five days later. There was a significant temporal association between stressful days and proteinuria (95% CI [0.22, 1.14]). The effect sizes of these associations were small, f = 0.04 and f = 0.12, respectively. Conclusions: Our findings suggest that psychological stress may trigger proteinuria in children with SSNS. Future research in larger samples is needed to support our findings.