A 2014 American Academy of Pediatrics (AAP) policy statement identified long-acting reversible contraceptives (LARCs) as first-line choices for adolescents, but pediatricians' current knowledge and practices about intrauterine devices (IUDs) and subdermal contraceptive implants (Implants) is unknown. We aimed to characterize pediatricians' knowledge and practices about LARCs for adolescents. Cross-sectional online survey emailed to a convenience sample of AAP member pediatricians in New York, Utah, Illinois, and Kansas in 2015 and 2016. The study included 561 practicing pediatricians. We measured knowledge about the suitability of IUDs and Implants for adolescents using two 7-item scales; a score of 7 indicates all correct. We dichotomized participants' scores as high and low knowledge if they scored ≥85% correct or <85%, respectively. Mean age was 47.4 (±11) years; 73% were female; and 72% general pediatricians. Almost all, 88%, counsel about contraception; 64% counsel about IUDs, and Implants, but only 4.1% insert them; 72% prescribe short-acting hormonal contraceptives; 44% had read the AAP policy statement. Mean score on the knowledge scale was lower for IUDs than for Implants (4.2 vs 5.1, respectively; P < .001). Multivariable regression analysis indicated that female pediatricians, adolescent medicine subspecialists, agreeing that pregnancy is a serious problem for adolescents in their practice, and having read the AAP policy statement predicted high knowledge about IUDs as well as Implants for adolescents. Most pediatrician respondents provided reproductive health care for adolescents and counseled about LARCs, but few inserted the devices. We identified knowledge deficits about suitability of IUDs for adolescents.