INTRODUCTION: The aim of the present study is to (a) describe the level of agreement between reports of health-related quality of life (HRQL) obtained from parents and young patients both on- and off-treatment and (b) explore the factors that may affect the level of agreement in the quality of life (QoL) between young patients and parental proxies. PATIENTS AND METHODS: The study group consisted of 149 young patients (77 children and 72 adolescents) with cancer followed up by an oncology in-patient clinic of a Greek children’s hospital with one of their parents (n=298). After parental consent was obtained, data were collected using the Pediatric Quality of Life Inventory (PedsQL) and a sociodemographic data form. RESULTS: The data collection showed that the best agreement was for the physical (ICC=0.82) and the school domains (ICC=0.68), whereas the worst was for the emotional (ICC=0.48) and the social domains (ICC=0.52). In the off-treatment group, the mother’s age was a significant predictor of the child-proxy difference on the physical sub-scale (F=9.804, P=0.003). There was a negative relationship between the mother’s age and patient proxy difference on the physical sub-scale. In the on-treatment group, the educational level of the father was found to be a significant predictor for the physical (F=4.30, P=0.041), school (F=5.51, P=0.022) and total sub-scales (F=10.41, P=0.002). Parents with basic education tended to have worse agreement with their children’s reports on the physical and school sub-scales, while parents with higher education had worse agreement with their children’s reports on the total sub-scale. CONCLUSIONS: Our findings suggest that the children and adolescents with cancer reported better QoL than their parents. The predictors found to be significant need to be examined extensively by further studies.