A 19-year-old man was admitted to our hospital for delayed puberty. At birth, he had macrocephalia and showed delayed physical and mental development. At 9 years of age, right cryptorchism was diagnosed. His parents had noticed that he could not recognize any smells since his infancy. Physical examination on admission revealed ocular hypertelorism, high myopia, high arched palate, and intermittent external strabismus. Sense of smell was scaled out by olfactometry. External genitalia were infantile. Neurological examination showed on IQ of 83, and mild truncal ataxia. Magnetic resonance imaging (MRI) showed a cystic distension of the IV ventricle, partial aplasia of the cerebellar vermis, elevation of the tentorium cerebelli, enlargement of the III ventricle, and agenesis of the corpus callosum. These findings revealed that the patient had Dandy-Walker malformation. The basal FSH, LH, and testosterone levels were all low compared with normal adult reference values. The serial LH-RH provocation tests showed stepwise LH and FSH elevation. After the fifth day of LH-RH administration, both LH and FSH responses clearly improved. Olfactory tracts were defective in MRI findings. These findings were consistent with hypogonadotropic hypogonadism of hypothalamic origin with anosmia, and the patient was therefore diagnosed with Kallmann syndrome. Sequence analysis of the KAL1 gene showed no mutation in the coding region. To our knowledge, this is the first case report of the coexistence of Kallmann syndrome and Dandy-Walker malformation in the same patient.