Of the Atlantic istiophorid billfishes, larval age–size relationships and growth rates have been examined only for blue marlin (Makaira nigricans). Using otolith microincrement analysis, we describe age–length and age–weight relationships for larval sailfish (Istiophorus platypterus) collected from the Straits of Florida. Sagittae and lapilli were dissected from 70 larvae ranging from 2.8 to 15.2 mm in (notochord or standard) length. Comparisons between otolith images obtained by light microscopy and scanning electron microscopy indicated that increment widths were well within the resolving power of light microscopy. Indirect evidence and published descriptions of larval blue marlin otoliths suggest daily increment deposition. Estimated ages of specimens ranged from 3 to 18 days. Length data were fitted to age estimates with an exponential model (R2 = 0.85). The estimated size-at-hatch for sailfish was 1.96 mm notochord length, and the daily instantaneous growth coefficient was 0.14. A power curve with exponent 3.05 described the length–dry weight relationship for sailfish. The instantaneous growth coefficient for an exponential regression of dry weight, converted from length, versus estimated age was 0.41. Growth in the length of sailfish larvae from the Straits of Florida was very similar to that described for blue marlin larvae from Exuma Sound, Bahamas.