Methotrexate (MTX) is a crucial part of the management of rheumatoid arthritis (RA). Although MTX is generally well tolerated, it is not exempt from adverse effects. The side effects of MTX are diverse, and pericarditis, as demonstrated in our case, is one of the rarest adverse effects. Therefore, it is crucial to rule out common causes of pericarditis, such as infections, malignancies, or other underlying conditions. However, once common causes are excluded, MTX-induced pericarditis should always be considered, and MTX should be discontinued without resumption due to potential relapse. Furthermore, the timing of MTX initiation is not significant; patients may have been on chronic MTX treatment or have recently started it. Moreover, pericarditis secondary to MTX is not exclusive to patients with rheumatological conditions but can also occur in other conditions.