Among other things, there are disclosed embodiments of a biopsy device using relative rotational motion to obtain a full-core biopsy sample. Inner and outer tubular members are provided connected to a handle. Each member includes a slit, and the members are rotatable with respect to each other. The device is inserted into a patient to a sampling site, and with the slits co-oriented, is extended into the sampling site. Tissue enters the tubular members through the slits, and one or both members are rotated to cut off and enclose tissue within the inner tubular member.