Huang LW, Wei JCC, Chen DY, et al. - In this study, the bidirectional relationship between macrophage activation syndrome (MAS) and systemic lupus erythematosus (SLE) was investigated using the 1997–2013 Taiwan’s National Health Insurance Research Database. From the whole beneficiaries, patients with newly diagnosed SLE from 2001 to 2013 were identified and individuals without SLE were selected from a one-million representative population. A total of 10,481 SLE patients and 20,962 PS-matched (1:2) non-SLE individuals were included finally. In this nationwide, population-based study, there appeared no significant correlation of a history of MAS with SLE risk. However, the risk of MAS was noted to be markedly linked with SLE and history of MAS.