The objective of this study was to investigate the relationship between change in positive and negative symptoms over time during haloperidol treatment. Subjects were 178 acutely exacerbating chronic schizophrenia patients participating in a clinical trial of haloperidol. Positive and negative symptoms were measured by the positive and negative symptom clusters of the Brief Psychiatric Rating Scale and by the Scales for the Assessment of Positive and Negative Symptoms. Hierarchical linear model analysis was used to estimate symptom-change trajectories of positive and negative symptoms over time in individual patients and to investigate the inter-relationship between these trajectories. Results indicate that positive and negative symptom-change trajectories over time were closely associated. This result did not depend on extrapyramidal side effects, depression, or the baseline balance of positive and negative symptoms. Thus, our study suggests that in acutely exacerbating schizophrenia patients, changes of positive and negative symptoms over time are related during the initial phase of the pharmacological treatment. This relationship may not extend to other treatment paradigms or beyond the initial phase of the treatment.