We have built a simple two-stage thermostat for measuring small-angle neutron scattering from liquids or solids in the vicinity of a phase transition. The thermostat was tested between 20 and 75 °C. The long-term temperature stability varies within ±0.2 and ±0.5 mK, depending on the set-point temperature. Positive and negative temperature steps of 0.5 mK and more can be obtained without overshoot. Small-angle neutron spectra from a binary ionic mixture in the critical domain are also reported. ©1997 American Institute of Physics.