PURPOSE: We describe two cases of intraoperative 4D microscope–integrated swept source optical coherence tomography (4D MIOCT) guided 27-gauge transvitreal retinochoroidal biopsy for choroidal melanoma. METHODS: Two 68-year-old females with choroidal melanomas underwent a transvitreal 27-gauge vitrectomy assisted chorioretinal biopsy for histologic and cytogenetic testing during I-125 radioactive episcleral plaque placement. A 4D (volumetric imaging through time) MIOCT device was used to simultaneously enable OCT image acquisition with surgical maneuvers during entry of and engagement of the vitreous cutter in the choroidal lesion. RESULTS: 4D MIOCT permitted real-time visualization of the choroidal tumor for selection of biopsy site in an area of adequate thickness and free of subretinal fluid, relatively perpendicular entry of the vitrectomy probe into the choroidal lesion, confirmation of adequate penetration depth prior to and during engagement of the vitreous cutter, and absence of subretinal fluid surrounding the retinotomy following removal of the probe. In both cases an adequate sample for histological and cytogenetic testing was obtained and no tamponade was required. CONCLUSION: Intraoperative 4D MIOCT imaging permits real-time visualization of vitreous cutter penetration and depth into the choroidal melanoma during a transvitreal choroidal biopsy.