Background: Obesity is a leading cause of cardiovascular disease mortality in the US population, and adequate physical activity has been shown to improve health outcomes for obese patients. The purpose of this study was to demonstrate the utility of accelerometry to quantify physical activity in people with achondroplasia, the most common short stature skeletal dysplasia. Methods: Twenty subjects with achondroplasia (18-50 years) wore an accelerometer while performing a sixminute walk test (6MWT) under standard conditions in a clinic setting and then nonstop for 7 days at home and also maintained a sleep and activity log. Time spent sleeping and different levels of physical activity were quantified by an accelerometer worn on the wrist based on cut-offs for activity counts per minute (cpm) derived from the 6MWT for moderate and vigorous physical activity. Sleep time was defined as any interval in which 8 of the prior 10 minutes registered zero activity counts, distinguishing it from sedentary activity. Results: New cutoff points generated for this cohort were 2009 -≤ 4607 (moderate activity) and ≥ 4608 (vigorous activity) cpm. Participants spent on average 33.4% of their days sleeping, 27.4% of the day in sedentary, 37.4% in light and <2% moderate and vigorous activity. For comparison, the unadjusted manufacturer activity cut-offs yielded 14.7% sedentary and 10.4% in moderate and vigorous activity. Conclusions: Accelerometry is an effective tool to assess physical activity in short statured individuals, but modifications are required and further study is needed.