Childhood onset schizophrenia (COS) and catatonia (C) are rare and severe psychiatric disorders. The aim of this study was to compare the phenomenology of COS with and without catatonia. We examined 33 cases consecutively referred to two major public university hospitals in Paris. There were 18 cases of COS (age=15.9+/-0.8 years) and 15 of COS+C (age=15.4+/-1.4 years). Patients were referred over the course of 3 and 9 years, respectively. Psychiatric assessment included socio-demographic, clinical and psychometric variables: the Brief Psychiatric Rating Scale (BPRS), the Scales for the Assessment of Positive (SAPS) and Negative Symptoms (SANS), and a catatonia rating scale. Patients with COS+C appeared to be more severely ill at admission and discharge compared with COS in nearly all clinical scores. They also exhibited significantly longer episode duration (50.8 weeks+/-4.8 vs 20.6+/-19.5). On the basis of multivariate logistic regression, the only clinical measure which significantly predicted group membership was the SANS Affective Flattening score (odds ratio=1.24; 95% CI=1.06-1.43). Our findings strongly suggest that catatonic COS differs from COS in ways that extend beyond motor symptoms. The SANS and SAPS scales, commonly used in schizophrenia, are not detailed enough to accurately describe catatonia in COS. The use of a catatonia rating scale is recommended to enhance recognition of and research into COS with catatonia.