Isolated congenital anosmia (MIM 107200) is a very rare condition characterised by a complete smelling defect that is present from birth in otherwise normal subjects. To our knowledge, nine sporadic cases of isolated congenital anosmia have been known,^1,2 and patients reported by Lygonis³ and those by us⁴ were only familial isolated congenital anosmia. Other cases of familial congenital anosmia had some additional manifestations^5–9 or had Kallmann syndrome. The defective smelling in isolated congenital anosmia may be attributed to the absence of olfactory function—that is, either replacement of the olfactory epithelium by respiratory epithelium,² or aplasia of the olfactory bulbs, sulci, and tract.¹ Diagnosis of isolated congenital anosmia is made by one or more of history, physical examinations, a standardised smelling test, computed tomography, magnetic resonance imaging, and biopsy of the nasal mucous tissue. Patients with isolated congenital anosmia had been unable to smell as back as they could remember, and had no history of other causes of anosmia, such as significant head trauma, neoplasm involving the olfactory system, or upper respiratory infection leading to damage of the olfactory epithelium. Physical examinations are useful to exclude an association of anosmia with other symptoms and to exclude secondary anosmia. A standardised smelling test confirms complete olfactory dysfunction. Computed tomography and magnetic resonance imaging may disclose other anomalies of the central nervous system, and biopsy may show abnormal replacement of the olfactory epithelium. An autosomal dominant mode of inheritance was suggested in a family reported by Lygonis³ and two families by us.⁴ However, nothing has been known for the disease gene localisation. Here we report the result of a genome-wide linkage analysis of the two unrelated Iranian families.