Pityriasis rubra pilaris (PRP) is a rare papulosquamous dermatosis in childhood, and its occurrence during anti-tumor necrosis factor therapy is exceptionally uncommon. We report a 9-year-old girl with juvenile idiopathic arthritis who developed biopsy-confirmed PRP after the third dose of adalimumab. Dermatological examination revealed widespread pruritic salmon-colored to erythematous finely scaly plaques, follicular accentuation, follicular hyperkeratotic papules, and focal islands of spared skin involving the trunk and upper extremities. Skin biopsy showed focal parakeratosis, irregular acanthosis, and prominent neutrophilic exocytosis at the follicular ostia, supporting the diagnosis of PRP. Alternative diagnoses, including paradoxical psoriasis and other papulosquamous or drug-related eruptions were considered; however, clinicopathological correlation favored PRP. The eruption resolved within three weeks after adalimumab discontinuation and recurred after re-exposure, supporting a probable adalimumab-associated paradoxical mechanism. The patient was subsequently switched to tocilizumab and achieved sustained clinical and laboratory remission without recurrence of cutaneous manifestations. This case emphasizes that PRP should be considered among rare papulosquamous eruptions occurring during anti-TNF therapy in children.