Objectives:To investigate whether there is an elevated neoplasm risk in patients with rheumatic diseases treated with conventional synthetic disease-modifying antirheumatic drugs (csDMARDs). Methods:A population-based nested case-control study was performed by retrieving all patients newly diagnosed with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and psoriatic arthritis (PsA) or psoriasis vulgaris (PsO) from the 2000 Longitudinal Health Insurance Database (LHID 2000) in Taiwan. Two hundred and sixty-one patients with neoplasm from 1997 to 2013 were enrolled in this study, and controls were matched in a 1:1 ratio with age, sex, and year of enrollment. Composition of demographic indices, comorbidities, medication usage, and differences in days of prescription of different medications between neoplasm and neoplasm-free (control) groups were compared. Results:Between the control and neoplasm groups, no differences in ratio were observed in the usage of hydroxychloroquine (50.96 vs. 49.04%,p= 0.6616), methotrexate (26.82 vs. 27.59%,p= 0.8441), azathioprine (3.45 vs. 3.07%,p= 0.8052), and cyclophosphamide (1.15 vs. 2.30%,p= 0.3131) from enrollment to index date. Medications within 3 years before the index date in patients that had >= 3 months of comparable duration also showed no difference (hydroxychloroquine: 33.06 vs. 30.25%,p= 0.6404; methotrexate: 20.66 vs. 25.21%,p= 0.4018; azathioprine: 2.48 vs. 2.52%,p= 0.9835; cyclophosphamide: 0.83 vs. 0.84%,p= 0.9906). We also made a subgroup analysis focusing on RA and SLE patients; no difference between control and neoplasm group in both the ratio of usage and days of prescription of hydroxychloroquine, methotrexate, azathioprine, and cyclophosphamide was observed. Conclusion:Neoplasm risk in patients with rheumatic diseases has no correlation with csDMARD usage.