OBJECTIVE: This study aimed to quantify the complexity of behavioral sequences of patients with schizophrenia and comparison subjects by using methods from nonlinear dynamical systems theory. METHOD: A simple choice task consisting of predicting 500 random right or left appearances of a stimulus was used to obtain binary response sequences in 22 patients with schizophrenia and 16 comparison subjects. Dynamical entropy was measured and the fluctuation spectrum of local subsequence entropies calculated to quantify the degree of interdependency between consecutive responses of patients and comparison subjects. RESULTS: The response sequences generated by the schizophrenic patients exhibited a higher degree of interdependency than those of comparison subjects. Moreover, schizophrenic patients exhibited significantly less consistency in their response selection and ordering, characterized by a greater contribution of both highly perseverative and highly unpredictable subsequences of responses within a test session. CONCLUSIONS: The result of the biological abnormality underlying schizophrenia may not be a simple increase or decrease of neuropsychological or neurobiological functions. Instead, the observed abnormalities in behavioral patterns reflect a quantifiable dysregulation and disorganization of these functions.Abstract Teaser