类风湿性关节炎（英文：Rheumatoid arthritis，简称RA），是一个主要影响关节的长期持续性疾病。它通常导致关节发热、肿胀和疼痛。疼痛和僵硬往往于休息后更恶化。最常见的是手腕和手涉及到身体两侧相同的关节。这个疾病也可能影响身体其他部分。这可能导致低红血球细胞、肺部炎症、和心脏炎症。也可能会发烧和缺乏活力。通常症状是逐渐超过数周至数月。

类风湿性关节炎的成因不明，但和基因与环境因素有关。作用机转为身体的免疫系统攻击关节，造成关节囊的发炎与增厚，通常也会影响到骨头和软骨。诊断方式大多根据病患的身体表征与症状。X光和实验室测试可以协助诊断或排除一些相似的疾病。如红斑性狼疮、干癣性关节炎，和纤维肌痛等疾病可能会有类似的症状。

Rheumatoid arthritis (RA) is a long-lasting autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involved, with the same joints typically involved on both sides of the body. The disease may also affect other parts of the body. This may result in a low red blood cell count, inflammation around the lungs, and inflammation around the heart. Fever and low energy may also be present. Often, symptoms come on gradually over weeks to months.