BACKGROUND Good syndrome (thymoma with immunodeficiency) is a frequently missed and forgotten entity. It is a rare cause of combined B and T cell immunodeficiency in adults. To date, fewer than 200 patients with Good syndrome have been reported in the literature. CASE REPORT We report a case of type AB Masaoka-Koga stage I thymoma which predated the evidence of immune dysregulation by 5 years, manifesting as bilateral cytomegalovirus retinitis, multiple bouts of pneumonia, and bronchiectasis in a HIV-seronegative 55-year-old man. Intravitreal ganciclovir was administered in addition to intravenous systemic ganciclovir, which resulted in severe neutropenic sepsis. A thorough immunodeficiency workup confirmed the presence of hypogammaglobulinemia with complete absence of B cells and reduced CD4/CD8 ratio. The patient responded well to monthly intravenous immunoglobulin replacement therapy, with no further episodes of infection since then. The immunoglobulin level doubled after 1 year of treatment. However, as the patient refused further intravitreal and CMV-targeted treatment, his vision did not recover. CONCLUSIONS Clinicians should be aware that thymoma can precede the onset of immunodeficiency. Clinical suspicion should be heightened in at-risk patients who present with multiple bouts of infection, particularly in thymoma cases with adult-onset immune dysfunction. It is of paramount importance to follow up those patients with annual clinical reviews and immunodeficiency screening.