In this prospective study, the developmental outcomes of 39 infants with high irritability and sensory processing problems, also described as regulatory disordered, were examined at 7–30 months and at 3 years using clinical interdisciplinary assessment. Infants with regulatory disorders were defined as being behaviourally difficult with disturbances in sleep, feeding, state control, self-calming, mood regulation and sensory processing. The performance of samples of infants with regulatory disorders, 13 untreated and 26 treated, and 11 normal children were compared at 3 years. All subjects in the clinical sample were offered 12 weeks of Intervention after the initial assessment to address regulatory problems. Of the 39 subjects, 26 chose treatment, thus resulting in a self-selected treated sample. Post hoc analysis revealed that, at 7–30 months, untreated subjects had more sleep problems and were more irritable whereas treated subjects had more feeding problems and their mothers reported feeling depressed. At 3 years, the children with regulatory disorders differed from their normal counterparts in sensory integration, mood regulation, attention, motor control, sleep and behavioural control. Untreated subjects showed more emotional and behavioural problems than treated subjects. Treated subjects had more motor and sensory integrative problems than untreated subjects but, despite the fact that they had more constitutional problems, they did not show the emotional and behavioural problems that were found in the untreated group. The clinical importance of these findings for occupational therapists is discussed.