Very narrow spontaneous emission (Deltalambda similar to 0.5 nm), corresponding to a quality factor Q in excess of 800, has been obtained under continuous-wave excitation at room temperature with an AlInN/GaN monolithic microcavity. The structure is made of thin ln(x)Ga(1-x)N/GaN (x = 0.15) multiple quantum wells inserted in a GaN 3lambda/2 (lambda = 420 nm) cavity surrounded by lattice-matched AlInN/GaN distributed Bragg reflectors.