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Objective: The objective of this paper is to clarify the demographic, clinical and serologic characteristics of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) overlap syndrome, known as ‘rhupus syndrome’. Methods: Between 1995 and 2012, 51 patients were classified as having rhupus among 3733 consecutive SLE patients. Rhupus was defined as a condition involving an overlap of RA and SLE features meeting the respective criteria of the American College of Rheumatology. The clinical and laboratory parameters of patients with rhupus syndrome were compared with those of 230 RA patients and 120 unselected SLE patients. Results: The age at the onset of rhupus was significantly younger than that of RA (p < 0.05), but similar to that of SLE. The initial manifestation was arthritis in 84.3% (43/51) of rhupus patients. Symptoms of SLE manifested after an average of 9.2 years. SLE was the initial diagnosis in 7.8% (four of 51) of patients, whereas both diseases developed simultaneously in 7.8% of the patients. SLE-associated manifestations were mild in rhupus syndrome, particularly neurologic disorders. Haematopoietic involvement was the most prominent systemic manifestation in rhupus patients. Conclusion: Rhupus syndrome constitutes a subgroup of patients with distinct demographic, clinical and immunological characteristics. RA typically presents first, and less-severe SLE-associated damage is apparent. [ABSTRACT FROM AUTHOR]