Objective. To investigate the prevalence of cognitive dysfunction in randomly selected patients with systemic lupus erythematosus (SLE).

Methods. Randomly selected, ambulatory patients with SLE (n = 49) or with rheumatoid arthritis (RA) (n = 40) completed neuropsychological tests. These included Associate Learning, Switching Attention, Continuous Performance, Associate Recall, Hand–Eye Coordination, Pattern Comparison, Pattern Memory, the Stroop Color and Word Test, and the Symptoms Checklist–90R. Results were evaluated by multiple linear regression analysis.

Results. SLE patients had poorer performance than RA patients on the test of attention (P = 0.002) and tests of visuospatial ability (P = 0.03 and P = 0.04), independent of age, education, or steroid use. The conservative level of statistical significance, adjusting for multiple comparisons, was 0.005. SLE patients reported more symptoms of cognitive difficulty.

Conclusion. Cognitive dysfunction is common in ambulatory SLE patients as measured by standardized tests and is a cause of distress and impaired functioning. Self-reported cognitive difficulty appears to correlate with objective performance.