The electron spin resonance lines of nitrogen impurity in diamond found by Smith, Sorokin, Gelles and Lasher have been re-examined in special samples and at low energy densities.The new spectral lines found have been analysed into three new systems: (i) Two more pairs of weak lines were found nearer to the main nitrogen lines. These lines are attributed to ¹³C atoms in some of the next nearest neighbour positions to the substitutional nitrogen. The principal hyperfine axes of the lines attributed by Smith et al. to the ¹³C atoms basal to the nitrogen of the N-C bond are found to be approximately parallel to the nitrogen hyperfine axes. (ii) Weak lines occur half-way between the main nitrogen lines. They are shown to be due to the interaction of the small quadrupole moment of the nitrogen with the electric field gradient. (iii) The lines due to the ¹⁵N with a nuclear spin of I = ½ have also been identified.