Extremely small monodisperse stimuli-responsive poly(N-vinylcaprolactam) (PVCL) colloidal gels with a radius of 45 nm were synthesized for the first time by surfactant-free precipitation polymerization in a high-pressure confined impinging jet reactor. We demonstrate that high pressures, combined with high mechanical shear forces inside the reaction chamber, resulted in size reduction and improved stabilization of microgel precursors leading to extremely small and uniform colloidal gels.