Purpose: The "Fragile X Messenger Ribonucleoprotein-1 (FMR1)" premutation (FXpm) is a genetic variant that is common in the general population and is associated with health symptoms and disease in adulthood. However, poor understanding of the clinical phenotype during childhood has hindered the development of clinical practice guidelines for screening and intervention. Given that social communication difficulties have been widely documented in adults with the FXpm and are linked with reduced psychosocial functioning, the present study aimed to characterize the communication profile of the FXpm during early childhood. Method: Eighteen children with the FXpm who were identified through cascade testing (89%) or screening at birth (11%) were compared to 21 matched typically developing children, aged 2-4 years. Participants completed standardized assessments of language (Mullen Scales of Early Learning) and adaptive communication (Vineland Adaptive Behavior Scales--II). Social communication was rated from seminaturalistic interaction samples using the Brief Observation of Social Communication Change. Results: Children with the FXpm showed delayed social communication development, with the magnitude of group differences highlighting social communication as a feature that distinguishes children with the FXpm from their peers (p = 0.046, [partial eta-squared] = 0.12). The groups did not differ on the standardized language and adaptive communication measures (ps > 0.297, [partial eta-squared]s < 0.03). Conclusions: Early screening and treatment of social communication delays may be key to optimizing outcomes for children with the FXpm. Further research is needed to replicate findings in a larger sample, delineate the trajectory and consequences of social communication difficulties across the life span in the FXpm, and determine the potential epidemiological significance of "FMR1" as a mediator of developmental communication differences within the general population.