Purpose To determine the choroidal thickness in the macular area in patients with idiopathic macular hole in one eye and an unaffected fellow eye and in healthy controls. Design Cross-sectional, prospective study. Methods Twenty-two patients with a full-thickness unilateral idiopathic macular hole and 22 age- and sex-matched controls were recruited. Enhanced depth imaging optical coherence tomography images were obtained by using spectral-domain optical coherence tomography. The choroidal thickness was measured in the subfoveal area and 1000 μm and 2000 μm away from the fovea in the nasal and temporal regions. The diameter of the macular hole and the axial length were determined. Results Choroidal thickness was significantly different across the 3 groups at all locations (P < .001, analysis of variance). The choroid was significantly thinner in eyes with idiopathic macular hole and in unaffected fellow eyes than in the control group (P < .01, Tukey-Kramer test). The mean subfoveal choroidal thickness was 183.2 μm in the idiopathic macular hole group, 196.6 μm in the fellow-eye group, and 245.0 μm in the control group. A negative correlation between subfoveal choroidal thickness and axial length was found in all groups (macular hole, r = -0.53, P = .01; fellow eyes, r = -0.56, P < .01; controls, r = -0.52, P = .01); in control eyes, a negative correlation was found between choroidal thickness and age (r = -0.48, P = .02). Conclusions Choroidal thickness was reduced in eyes with idiopathic macular hole and also in fellow unaffected eyes. This may suggest a contributing role of the choroid in the pathogenesis of idiopathic macular hole.