Background: Paraneoplastic neurological syndromes have diverse clinical presentations and offer an opportunity for early diagnosis of malignancy and treatment. Recently, a new paraneoplastic syndrome associated with seminoma was described, consisting of rhombencephalitis with antibodies targeting the Kelch-like protein 11 (KLHL11). Questions were raised as to the spectrum of clinical symptoms and strength of association to seminoma. Methods: We present a 45-year-old man with bilateral sensorineural hearing loss, vertigo, and progressive ataxia. An extensive diagnostic workup led to the diagnosis of anti-KLHL11 paraneoplastic syndrome based on an immunofluorescence assay showing a typical pattern and a confirmatory serological assay. As a result, the patient underwent a meticulous search for an underlying seminoma. Results: Although initially, all images were interpreted as negative, a revision of the positron emission tomography-CT (PET-CT) examination identified a small mediastinal suspicious mass. The mass was resected, and pathological examination confirmed it to be an extra-testicular seminoma. Conclusions: Patients presenting with progressive sensorineural hearing loss, vertigo, and ataxia should be evaluated for KLHL11 paraneoplastic syndrome. Furthermore, we support a strong association between anti-KLH11 rhombencephalitis and an underlying seminoma and recommend a thorough search for an undiagnosed germ cell tumor in these patients.