The 'Roja Arequipeña' onion is a bulb of strong astringent flavour, useful for preparing a great variety of typical Peruvian foods. Arequipa, the second most important city of Peru after the capital Lima, is the main producer of onions in Peru. Monoculture practices encourage the infestation of nematodes and fungi in fertile Arequipean soils, that severely affect the yields of onion crops. Soilless culture is a technique that can relieve this problem because it permits the intensive onion production in monoculture. To prove that it is possible to grow onion in soilless systems, onion seedlings were planted in different natural substrates from Arequipa: rice hulls and pumice. The substrates tested were: pumice (100%), rice hulls (100%) and three mixtures of pumice and rice hulls: 70%:30%, 50%:50% and 30%:70%. The plants were watered with nutrient solution prepared with La Molina hydroponics solution. Significant differences were found in the diameter, fresh weight and dry weight of the bulbs, yield and pungency. The highest yield (60 g/plant or 28.64 Tn/Ha) was obtained with pumice (100%) and the lowest yield (40 g/plant or 16.76 Tn/Ha) with rice hulls (100%). The highest pungency (15.0 μmol pyruvic acid/g fresh weight) was obtained with the 30%:70% pumice: rice hulls mixture and the lowest pungency (12.8 μmol pyruvic acid/g fresh weight) with rice hulls only. Finally, to demonstrate the economical feasibility of onion hydroponic production, a profitability analysis was made. The only treatment that had a negative profitability was the 100% rice hulls substrate.