Natural convection from a horizontal cylinder dissipating a uniform heat flux is analyzed by solving the full two-dimensional Navier-Stokes and energy equations. For Pr=- 0.7 flow fields and transport results are determined in the range 10-2≤ Ra* ≤ 107, For Ra* ≤ 0.1 the surface temperature variation becomes less than 5% and the uniform heat flux and isothermal boundary conditions become equivalent. A correlation for the average Nusselt number is suggested. Some experimental data are also reported. The agreement between the computed and measured transport results is found to be very good.