Steroid induced psychosis in SLE is rare but clinically important, and often difficult to distinguish from lupus cerebritis. We report a patient with SLE who became depressed following an increase in her steroid dosage. Based on her clinical presentation and high levels of antibodies to P ribosomal proteins (both in CSF and serum) a diagnosis of lupus cerebritis was made. Steroid dosage, time intervals, and the duration of mental changes may help in differentiating steroid psychosis from lupus cerebritis. No single laboratory test sufficient to establish a definitive diagnosis of lupus cerebritis is available at the present time. However, elevated levels of antibodies to P ribosomal proteins may assist in confirming the diagnosis of this condition.