Compounds and molecular fragments were analyzed regarding structural diversity, complexity, atoms, and ring content. The structural diversity was evaluated with the pairwise similarity values calculated with the Tanimoto coefficient, for both Morgan fingerprints with radius 2 (Morgan2, 1024-bits) and radius 3 (Morgan3, 1024-bits), and Molecular ACCes System (MACCS) keys (166-bits). The structural differences between compound and fragment datasets were evaluated by comparing the profiles of 14 descriptors: number of atoms of carbon, nitrogen, oxygen, and heavy atoms, the number of rings and heterocycles (both aliphatic and aromatic), spiro atoms, bridgehead atoms, the fraction of sp 3 carbons, and chiral carbons.