Sponges are an important component of the benthic community, especially on coral reefs, but demographic data such as growth, recruitment or mortality are notably limited. This study examined the growth of the elephant ear sponge Ianthella basta, the largest and in some areas one of the dominating sponge species on Guam and other pacific reefs. We measured growth rates of the natural population on Guam over the course of one year and identified intra-individual growth patterns. Initial sponge sizes ranged from 200 to 35,000 cm2. Specific growth rates ranged from 0.08 to 6.08 with a mean specific growth rate of 1.43 ± 1.29 (SD) year-1. Furthermore, specific growth decreased with sponge size. The age estimate for the largest sponge (1.7 m height 9 9.5 m circumference) was *8 years. Intra-individual growth was mostly apical. This study demonstrated high growth rates, which has notable implications for environmental assessments, management and potential biomedical applications.