This paper estimates the uncertainty in the National Hurricane Center (NHC) best track parameters for Atlantic basin tropical and subtropical cyclones. A survey of NHC Hurricane Specialists was conducted to assess the uncertainty in best track parameters, and the results were compared with a similar survey conducted a decade earlier. The results show that the uncertainty in best track parameters has decreased over time, particularly for intensity and position. The uncertainty in intensity is about 12 kt for tropical storms, 14 kt for category 1 and 2 hurricanes, and 10 kt for major hurricanes when based on satellite-only observations. For position, the uncertainty is about 35 n mi for tropical storms, 25 n mi for category 1 and 2 hurricanes, and 20 n mi for major hurricanes. The uncertainty in central pressure is about 6 mb for tropical storms, 8 mb for category 1 and 2 hurricanes, and 10 mb for major hurricanes. The uncertainty in wind radii is about 40 n mi for tropical storms, 30 n mi for category 1 and 2 hurricanes, and 25 n mi for major hurricanes. The results suggest that the uncertainty in best track parameters is relatively small compared to the actual values, and that the NHC's best track analyses are generally accurate. The results also indicate that the uncertainty in best track parameters is likely to decrease further with the availability of more data and improved observational techniques. The implications of these results for NHC analysis and forecast products, as well as for the Hurricane Forecast Improvement Program, are discussed.This paper estimates the uncertainty in the National Hurricane Center (NHC) best track parameters for Atlantic basin tropical and subtropical cyclones. A survey of NHC Hurricane Specialists was conducted to assess the uncertainty in best track parameters, and the results were compared with a similar survey conducted a decade earlier. The results show that the uncertainty in best track parameters has decreased over time, particularly for intensity and position. The uncertainty in intensity is about 12 kt for tropical storms, 14 kt for category 1 and 2 hurricanes, and 10 kt for major hurricanes when based on satellite-only observations. For position, the uncertainty is about 35 n mi for tropical storms, 25 n mi for category 1 and 2 hurricanes, and 20 n mi for major hurricanes. The uncertainty in central pressure is about 6 mb for tropical storms, 8 mb for category 1 and 2 hurricanes, and 10 mb for major hurricanes. The uncertainty in wind radii is about 40 n mi for tropical storms, 30 n mi for category 1 and 2 hurricanes, and 25 n mi for major hurricanes. The results suggest that the uncertainty in best track parameters is relatively small compared to the actual values, and that the NHC's best track analyses are generally accurate. The results also indicate that the uncertainty in best track parameters is likely to decrease further with the availability of more data and improved observational techniques. The implications of these results for NHC analysis and forecast products, as well as for the Hurricane Forecast Improvement Program, are discussed.