The Cyclotron Corporation has been actively engaged in the design, development and construction of particle accelerators for neutron radiotherapy. Our work includes the construction of a deuterium-tritium ( D-T ) neutron generator for isocentric mounting, the installation of two cyclotrons with isocentrically mounted targets using the 9Be( d, n) reaction with deuteron energies up to 15 MeV and most recently the development of compact single particle cyclotrons with an isocentric target using the 9Be( p, n) reaction with proton energies up to 35 MeV. This paper discusses the effort in each of these areas with a summary of their neutron yield and depth dose characteristics. Also presented are the most recent measurements of neutron yield, depth dose, skin sparing and gamma contamination from the 9Be(p, n) reaction which shows that a compact cyclotron system can be used to produce neutrons with therapy characteristics exceeding those obtainable from present 60Co γ-radiation equipment.