Implantation of radiotransmitters in juvenile carnivores allows researchers to study little-known life stages. In the field, we successfully implanted 7 mountain lion (Puma concolor) kittens from 2 litters in the Santa Monica Mountains (Los Angeles and Ventura Co., CA), 1 in 2004 and 1 in 2010, with intraperitoneal very high frequency radiotransmitters. We used Global Positioning System location data downloaded from their mothers' collars to locate the dens in their absence, and we hand-captured the kittens at 3–4 weeks of age. The implant surgery proceeded without complication and the mothers returned promptly afterward. The transmitters allowed us to track these young mountain lions for 13–17 months, from neonates to subadults. Upon necropsy of 3 of the individuals as subadults, the implants appeared to have had no negative impacts on the animals. Implantable radiotransmitters provided a safe and effective method for following young mountain lions. © 2012 The Wildlife Society.