The combined effects of flame stretch, curvature, and radiation on the extinction of premixed tubular flames are investigated using the large-activation-energy asymptotic analysis. A general theoretical correlation for flame radius, speed, and temperature is obtained and used to study the combined effects on the flame extinction limit. The flame isola for radiative tubular flames is predicted and it is found that both extinction limits are strongly affected by flame curvature. By varying the radiation intensity, various flame bifurcations are predicted and curvature effects are examined. It is shown that the extinction limits can be greatly changed by the change of flame curvature. Furthermore, the effects of Lewis number are examined. The results demonstrate a significant influence of preferential diffusion on the extinction limits of tubular flames at different curvatures.