A retrospective analysis of a French registry including patients with cancer treated with immune checkpoint inhibitors revealed six cases of rheumatoid arthritis (RA) and four cases of polymyalgia rheumatica (PMR), which developed at a median of 1 month after exposure. Three patients who developed RA required DMARD therapy; the other three cases were treated with corticosteroids or NSAIDs. All four patients with PMR responded to corticosteroids.