Developmental regression in children, in the absence of neurological damage or trauma, presents a significant diagnostic challenge. The complexity is further compounded when it is associated with psychotic symptoms.

We discuss a case series of ten children aged 6–10 years, with neurotypical development, presenting with late-onset developmental regression (>6 years of age), their clinical course and outcome at 1 year. A comprehensive clinical evaluation, laboratory investigations and neuroimaging ruled out any identifiable neurological cause.

Mean age at regression was 7.65 (s.d. 1.5) years and mean illness duration was 10.1 (s.d. 8.5) months. The symptom domains included regression (in more than two domains – cognitive, socio-emotional, language, bowel and bladder incontinence), emotional disturbances, and hallucinatory and repetitive behaviours. Response to treatment was gradual over 6 months to 1 year. At 1-year follow-up, nine children did not attain pre-regression functioning, and residual symptoms included not attaining age-appropriate speech and language, socio-emotional reciprocity and cognitive abilities.

These cases demonstrate a unique pattern of regression with psychiatric manifestations, distinct from autism spectrum disorder and childhood-onset schizophrenia. The diagnostic dilemma arises from the overlap of symptoms with childhood disintegrative disorder (CDD), childhood-onset schizophrenia and autism. This study underscores the diagnostic intricacies of this clinical presentation and highlights the need for longitudinal follow-up to unravel the transitions in phenomenology, course and outcome. For severe manifestations such as developmental regression, where the illness is still evolving, considering CDD as a non-aetiological and transitory/tentative diagnosis would aid against premature diagnostic categorisation and provide scope for ongoing aetiological search.