Seed ethanolic extracts of 21 Brazilian plants were evaluated for ovicidal, larvicidal, and pupicidal activities against insecticide-susceptible (SS) and field-collected (FC) strains of Aedes aegypti (L.) (Diptera: Culicidae), as well as for their effects on nontarget organisms. Myracrodruon urundeuva Fr. Allemao extract was highly toxic to both mosquito strains. Schinopsis brasiliensis Engler extract showed low toxicity and was 38-68 times less toxic to Ae. aegypti larvae than was M. urundeuva extract. The pupicidal activity (LC50) of 14 plant seed extracts ranged between 9 and 433/g/ml, and toxicities were comparable to both mosquito strains. Piptadenia moniliformis Benth. and Luetzelburgia auriculata (Allemao) Ducke extracts showed the highest activities against pupae of FC and SS strains. None of the extracts showed 100% ovicidal activity. In addition, the active extracts did not show high acute toxicity to mice (LD50 > 1.5 g/kg), except that of Enterolobium contortisiliquum (Vell.) Morong. Most of the active extracts exhibited low toxicity against brine shrimp (Artemia sp.) nauplii. The extracts of M. urundeuva, P. moniliformis, and L. auriculata are promising sources of recognized classes of insecticidal compounds with good selectivity against immature stages of Ae. aegypti.