Electron spin resonance studies have been made of natural diamond crystals electron‐irradiated at room temperature. A radiation‐induced spectrum is identified as arising from a new anisotropicS=1 center. TheS=1 center is characterized by:g1=2.0026, g2=2.0021, g3=2.0016; D1=∓27(10−4 cm−1), D2=∓25(10−4 cm−1), D3=±51(10−4 cm−1). Associated with each resonance line are four sets of weaker lines which are ascribed to hyperfine interaction with13C (I=½, 1.1% abundant) at four nonequivalent sets of sites. The identity of the defect has not yet been established.