• Of importance, •• Of major importance 1,3-Diphenyl-4,5-dihydro-1H-pyrazol-5-one In the title pyrazolone derivative, C(15)H(12)N(2)O, the five-membered ring is approximately planar (r.m.s. deviation = 0.018 Å), and the N- and C-bound benzene rings are inclined to this plane [dihedral angles = 21.45 (10) and 6.96 (10)°, respectively] and form a dihedral angle of 20.42 (10)° with each other. Supra­molecular layers are formed in the crystal structure via C—H⋯O and C—H⋯N inter­actions, and these are assembled into double layers by C—H⋯π and π–π inter­actions between the pyrazole and C-bound benzene rings [ring centroid–centroid distance = 3.6476 (12) Å]. The double layers stack along the a axis being connected by π–π inter­actions between the N- and C-bound benzene rings [ring centroid–centroid distance = 3.7718 (12) Å]. In the title pyrazolone derivative, C 15 H 12 N 2 O, the fivemembered ring is approximately planar (r.m.s. deviation = 0.018 Å ), and the N-and C-bound benzene rings are inclined to this plane [dihedral angles = 21.45 (10) and 6.96 (10) , respectively] and form a dihedral angle of 20.42 (10) with each other. Supramolecular layers are formed in the crystal structure via C-HÁ Á ÁO and C-HÁ Á ÁN interactions, and these are assembled into double layers by C-HÁ Á Á andinteractions between the pyrazole and C-bound benzene rings [ring centroid-centroid distance = 3.6476 (12) Å ]. The double layers stack along the a axis being connected byinteractions between the N-and C-bound benzene rings [ring centroid-centroid distance = 3.7718 (12) Å ].