Catatonia is a neuropsychiatric disorder characterized by abnormalities of movement, communication, and behavior, often accompanied by a disturbance of mood, thought and perception. If untreated, it may lead to serious complications, including death. Although often described in adults with schizophrenia and severe mood disorders, it can also occur in persons with neurodevelopmental disorders (NDD), particularly autism spectrum disorder (ASD). Since its diagnosis is more likely to be missed by clinicians with limited experience, we attempted to determine if experienced psychiatrists can make a reliable diagnosis of catatonia in a group of patients with NDD. Twenty patients with catatonia with ASD/NDD (12 males 8 females; age range 13-34 years; mean 17.5; SD 4.8), diagnosed by two American psychiatrists, were re-evaluated by a group of Swedish psychiatrists. In the initial round, agreement was reached in 15 (75%) cases. However, a careful review of additional material and several virtual discussions were required to reach agreement in the remaining 5 (25%) of cases. The diagnosis of catatonia in individuals with NDD is challenging, even for experienced clinicians. Reasons for the lack of diagnostic agreement in the five patients are discussed to highlight the barriers for accurately diagnosing catatonia in patients with NDD.