It is a challenge to use collars on male cervids because their neck size can increase substantially during the rut and also because of growth as the animal matures. We describe how to build a self-adjusting expandable collar for yearling or adult male Rocky Mountain elk (Cervus elaphus) to which very high frequency transmitters and global positioning system (GPS) units can be attached. We evaluated performance and durability of 35 expandable collars placed on male elk from 2009 through 2011 within the Starkey Experimental Forest and Range enclosure, Northeast Oregon, USA. Twenty-four (69%) collars remained on elk throughout our sampling period for GPS fixes from March or April to 1 November each year. Eight (23%) collars broke before 1 November and 3 (9%) collars were removed when males were harvested by hunters. Six of 8 collars that broke before 1 November came off during the rut. Mean date these collars broke was 19 September (SE = 7.1 days, 95% CI = 1 Sept. to 7 Oct.). Excluding 1 collar still being worn by a male elk and those collars either recovered when males were harvested by hunters (3) or removed from adult males on the winter feed ground (7), mean number of days collars stayed on was 279 (SE = 25.5, 95% CI = 225.8–331.3 days). No deaths or injuries were attributed to the collars. Because these collars can break, especially during the rut, we recommend sample sizes of males be increased ≥25% to compensate for collars that may come off during that period. Collars are not recommended for multi-year studies of male elk without substantial modifications to our design and further testing. © 2013 The Wildlife Society.