  We have observed the rare decay B0->rho+rho- in a sample of 89 million BBbar
pairs recorded with the BABAR detector. We measure the branching fraction
B(B0->rho+rho-)=(27+7-6+5-7)10^-6 and determine the longitudinal polarization
fraction Gamma_L/Gamma=0.99+0.01-0.07+-0.03. Our results are preliminary.
