An increased understanding of dietary protein for growth and development of Lytechinus variegatus would increase our knowledge of the nutritional requirements of sea urchins and contribute to the development of formulated feeds for the aquaculture of commercially important sea urchin species. Previously starved urchins (ca. 36 mm diameter, n = 12) were held in replicated (3×) 80-l aquaria with artificial seawater at 22 ± 2 °C and 32‰ salinity. Urchins were fed one of three diets containing 9%, 20% or 31% dry protein ad libitum for 65 days. Sea urchins fed diets containing 9% protein consumed more food than urchins fed 20% or 31% protein diets. Sea urchins fed the 9% protein diet had greatly decreased survival. Test diameters increased significantly from the initial sample only in those sea urchins fed the 20% protein diet. Sea urchins fed the 20% protein diet had larger test diameters than those fed the 9% but not the 31% protein diet at day 65. Urchins fed the 20% protein diet had significantly greater total wet and dry weights than urchins fed the 9% but not the 31% protein diet. At the conclusion of the study there were no significant differences in lantern, gut or gonad wet or dry weight for urchins fed the three diets (test dry weight was highest at 20% protein). Specific growth rate, estimated dry matter production and production efficiency in urchins fed the 20% protein diet were greater than in urchins fed the 9% but not the 31% protein diet. Urchins fed the 9% or 20% protein diet utilized dietary protein more efficiently than urchins fed the 31% protein diet. Gonad production was not different among diets but gonad production efficiency was significantly lower in urchins fed the 9% protein diet. Data suggest that adult L. variegatus utilizes the 20% protein diet most efficiently and that this diet would be the most cost-effective of the diets tested. © 2005 Elsevier B.V. All rights reserved.