Gray matter (GM) mask for human and chimpanzee structural T1-weighted magnetic resonance imaging (MRI) scans The human mask was created using the GM tissue segment map from the CAT12 (Computational Anatomy Toolbox) tissue probability map (TPM) and shooting template. Using a probability threshold of 0.2 voxels within both segment maps were included in the mask. Finally, single voxels that did not touch any other voxel were removed during clean up. The chimpanzee GM mask was created using the chimpanzee TPM (Vickery et al., 2020) provided with CAT12.7+ at a GM probability threshold of 0.3. The human GM mask is provided at a resolution of 1.5mm and 3mm while the chimpanzee GM mask at a resolution of 1mm and 2mm. We also provide a cortex GM mask containing the cerebral cortex and basal ganglia for both species with the cerebellum and brain stem removed. Cerebellum and brain stem are removed using the chimpanzee Davi130 parcellation (Vickery et al., 2020) in chimpanzees and for human the parcellation registered to MNI space. Version 2: A new human cortex and sub-cortex GM mask created from the 1.5mm "CAT12_IXI555_MNI152_TMP_GS_GMprob0.2_clean.nii.gz" mask by using the Schaefer 1000 parcellation (Scaefer et al., 2018) for the cortex mask and Tian sub-cortex atlas (Tian et al., 2020) for the sub-cortex mask. A shell script "cortex_subcortex_mask.sh" outlines the steps taken to create the GM mask.