PURPOSE: Chronic sorrow is a multidimensional concept experienced by mothers of children suffering with chronic conditions, e.g. cancer. Little is known about the concept of chronic sorrow and related issues/experiences among mothers of children with cancer living in Iran. This study aimed to explore the concept of chronic sorrow, based on the lived experiences of chronic sorrow experienced in a group of Iranian mothers of children with cancer. METHODS: In this hermeneutic phenomenological study, 8 mothers of children with cancer participated in semi structured, in-depth interviews about their experiences of chronic sorrow. Interviews continued until data saturation was reached. All interviews were recorded, transcribed, analyzed, and interpreted using the seven steps of the Dickelman et al.’s phenomenological approach. RESULTS: The three main themes that emerged from mothers’ experiences of chronic sorrow related to their child’s cancer were "climbing up shaky rocks," "religious fear and hope," and "continuous role changing." Each of these themes consisted of several subthemes. Besides the possibility of growth and coping with the chronic condition of a child which has been seen in other studies on chronic sorrow experiences, religious issues were more profound than what has reported in Western studies. Also the ambiguous prognosis and uncertain process of the cancer in children had made the experience of chronic sorrow more unique. CONCLUSION: The results of this study show that the experiences of mothers of children with cancer in Iran are not specific to them, but are better comprehended in their traditional socio-cultural context.