Objective: P50 suppression refers to the P50 ERP amplitude-reduction to the second (S2) relative to the first (S1) of identical brief auditory stimuli (SOA = 500 ms). Its reduction in schizophrenia is argued to represent impaired inhibitory input (II) mechanisms. Enhancing attention enhances II functionality (reducing S2P50 amplitude and increasing P50 difference) in healthy subjects. We determined whether the effect of attention on P50 suppression differs between schizophrenia patients (SCZ) and controls (CON) and thus is a confound in P50 schizophrenia research. Methods: We manipulated the direction of attention (attention, non-attention) in 21 SCZ and 18 CON in the P50 suppression task. Results: Directing attention towards stimulus pairs (versus non-attention) increased P50 suppression (P50 difference). This effect differed between groups, with attention increasing S1P50, reducing S2P50 and increasing P50 suppression (P50 difference and reducing P50 ratio) in CON only. No group differences were found for P50 difference or ratio. Conclusions: Attention is a confound in schizophrenia P50 research and thus should be carefully controlled. When attention was controlled, P50 group differences were not found. Significance: The SCZ-CON P50 difference reported in the literature may be related to uncontrolled attention (and not impaired P50 suppression per se).