Background: Ocular involvement is relatively common in granulomatosis with polyangiitis (GPA); however, choroidal involvement is rare. We present a case of serous retinal detachment resulting from choroidal involvement in GPA. Case presentation: A 55-year-old male presented to our clinic with bilateral eye redness and pain. Ocular examination revealed bilateral conjunctival injection, and dilation of the episcleral and scleral vessels. Slit-lamp examination revealed anterior chamber cells. Optical coherence tomography (OCT) confirmed serous retinal detachment (SRD) in the left eye. The patient had recently been diagnosed with GPA following a lung biopsy and had received immunosuppressive therapy, including systemic steroids, cyclosporine, mycophenolate mofetil, and rituximab. Five weeks after treatment, the clinical symptoms of the patient, including SRD, improved with alleviation of systemic symptoms. However, tapering systemic steroids and immunosuppressants and discontinuing rituximab led to disease reactivation. OCT demonstrated a recurrence of subretinal fluid, which had previously resolved, and slit-lamp examination showed mild bilateral engorged scleral vessels. Conclusions: Choroidal involvement can present as SRD and may indicate disease activity in patients with GPA.