Burrows are critical refugia for desert tortoises (Gopherus agassizii), buffering individuals from extreme temperatures and desiccation. This buffering is crucial over winter when surface temperatures can fall below freezing and tortoises remain largely inactive, surviving on limited energy and water reserves. While burrow use is well documented, less is known about how burrow structure and microclimate vary across life stages during overwintering. We compared burrow structure and microclimate used by adult and juvenile tortoises over two winters in the Mojave Desert. Microclimate data were collected using temperature and humidity loggers affixed to tortoises, representing the conditions experienced during brumation, spent primarily in their chosen winter burrow. On average, juveniles used shorter, narrower burrows and experienced lower temperatures, higher relative humidity, and lower vapor pressure deficits than adults. This suggests the narrower burrow structure and associated microclimate experienced by juveniles partially compensate for the greater water-loss susceptibility of juveniles due to their higher surface area-to-volume ratios. These results reveal ontogenetic differences in burrow structure and highlight that juvenile tortoises can access hydric microclimates equal to or more favorable than those available to adults. Juveniles may possess greater resilience to dry conditions than would be expected based solely on their physiological vulnerability.