PURPOSE: Occult macular dystrophy (OMD) is an inherited macular dystrophy characterized by a progressive macular dysfunction without any visible fundus abnormality. We studied the foveal thickness in patients with OMD using optical coherence tomography (OCT). DESIGN: Observational case series. Foveal thickness by OCT images. METHODS: Foveal thickness obtained from 22 eyes of 11 patients with OMD was compared with that from 27 eyes of 20 age-matched normal controls. RESULTS: Mean foveal thickness in the patients group (96.5 +/- 19.5 microm) was significantly thinner than that in the normal controls (133.3 +/- 9.0 microm, P <.0001, Mann-Whitney U test). Eighteen of 22 eyes with OMD had foveal thickness that were thinner than the lower limit of the normal range. There was no statistically significant correlation between the foveal thickness and visual acuity, age, or duration from onset. CONCLUSION: These results demonstrated that there are significant anatomic changes in the macula of patients with OMD.