Development of a standardized reference diet will facilitate the determination of nutritional requirements for sea urchins. A purified diet, containing only chemically defined ingredients, provides consistency in diet formulations for reproducibility across different laboratories. In the present study, the growth performance of small Lytechinus variegatus (11.9 ± 1.3 g [mean ± SD] wet weight, 28.4 ± 1.1 mm test diameter; 16 per treatment) fed ad libitum daily (16 weeks) one of seven purified diets differing in the level (0, 2.4, or 4.8% as fed) and source of neutral lipid (refined menhaden oil and soy oil) was compared with the growth performance of individuals fed a semipurified diet previously shown to support high growth rates and gonad production. Survival was ≥88% for all dietary treatments, and the growth rates of individuals fed the 1.2% menhaden oil and 1.2% soybean oil purified diet (215% wet weight gain) were approximately 65% of those for individuals fed the semipurified diet (326% wet weight gain). The growth rates and wet organ weights for individuals fed purified diets were not significantly affected by lipid source. However, increased total dietary lipid resulted in higher dry gut weights. Ovary weight was higher than testis weight for all treatments. Although no significant differences were detected among the purified diet treatments, qualitative performance (survival, weight gain, and gonad production) for individuals fed the purified diet containing 1.2% menhaden oil and 1.2% soybean oil was best under the conditions of this study. The purified diet used in this study is adequate to evaluate specific nutrients on sea urchin weight gain and organ production. © American Fisheries Society 2013.