Study objective To determine the effect of a 9-mm diameter carbon dioxide cryoprobe, the Endocryo, on myomas and endometrial/myometrial tissue in vitro. Design Comparative laboratory study (Canadian Task Force classification II-2). Setting University laboratory. Patients Women with and without myomas, undergoing hysterectomy. Intervention A single 5-minute freeze followed by an active thaw was applied to uterine myomas and endometrial/myometrial tissue in vitro. Measurements and main results Endometrial/myometrial and uterine myoma temperature change was measured continuously during the cryosurgical procedure. Depth of cell death was measured using nicotinamide adenine dinucleotide diaphorase enzyme assay. There was no significant difference in temperature change and depth of cell death between myomas and endometrial/myometrial tissue in vitro. Conclusions The Endocryo produces the same cryosurgical effect on both uterine myomas and endometrial/myometrial tissue in vitro, an important principal for future development of a clinically effective cryosurgical device for the treatment of menorrhagia in the presence of submucous myomas.