Recently, a great deal of attention has been focused on investigating whether decreased ages and sizes at maturation in exploited fish populations could be evolutionary responses to selective fishing. To this end, the main focus has been on isolating the effects of growth changes from the process of maturation, but little effort has been invested in assessing how growth actually affects ages and sizes at maturation in a population. Here, we develop a probabilistic description of the process of maturation, which makes explicit the mathematical links between maturation, growth and the probabilistic maturation reaction norm. Apart from providing a mathematically explicit yet heuristically simple framework for assessing the role of growth in the age and size at maturation, we demonstrate by simulation that changes in growth rates can result in considerable shifts in the age and size at maturation. Focusing more attention on growth histories of individuals would provide a better position to understand the processes constituting phenotypic shifts in the age and size at maturation and help in disentangling environmentally induced plastic changes in maturation from those caused by evolutionary responses to fisheries-induced selection.