Background: This study investigates the posited relationship between learning to read, and internalizing and externalizing problem behaviours, during the transition from preschool to primary school. Methods: A total of 196 (104 boys, 92 girls) children participating in the Jyvaskyla Entrance into Primary School (JEPS) study were followed up six times during their transition from preschool to primary school. At each measurement, the children's reading performance was tested. Moreover, their internalizing and externalizing problem behaviour was examined by means of structured interviews. Results: The results showed that problems in reading acquisition predicted an increase in internalizing problem behaviour during the preschool year and first grade, whereas during the second grade they were associated with an increase in subsequent externalizing problem behaviour. Moreover, from preschool to the beginning of the primary school internalizing problem behaviour predicted subsequent externalizing problem behaviour. Later on during the first and the second primary school years, it was externalizing problem behaviour that predicted an increase in internalizing problem behaviour. Conclusions: The results of this study suggested that difficulties in learning to read, and internalizing and externalizing problem behaviours are developmentally linked in a cumulative manner.