White matter alterations have been reported in children with prenatal alcohol exposure (PAE) and in children with attention deficit hyperactivity disorder (ADHD); however, as children with PAE often present with ADHD, covert PAE may have contributed to previous ADHD findings. Additionally, data regarding intracortical myelination in ADHD are lacking. Therefore, we evaluated intracortical myelination (assessed as the T1w/T2w ratio at 4 cortical ribbon levels) and myelin-related deep white matter features in children (aged 8-13 years) with ADHD with PAE (ADHD + PAE), children with familial ADHD without PAE (ADHD-PAE), and typically developing (TD) children. In widespread tracts, ADHD + PAE children showed higher mean and radial diffusivity than TD and ADHD-PAE children and lower fractional anisotropy than ADHD-PAE children; ADHD-PAE and TD children did not differ significantly. Compared to TD children, ADHD + PAE children had lower intracortical myelination only at the deepest cortical level (mainly in right insula and cingulate cortices), while ADHD-PAE children had lower intracortical myelination at multiple cortical levels (mainly in right insula, sensorimotor, and cingulate cortices); ADHD + PAE and ADHD-PAE children did not differ significantly in intracortical myelination. Considering the two ADHD groups jointly (via non-parametric combination) revealed common reductions in intracortical myelination, but no common deep white matter abnormalities. These results suggest the importance of considering PAE in ADHD studies of white matter pathology. ADHD + PAE may be associated with deeper, white matter abnormalities, while familial ADHD without PAE may be associated with more superficial, cortical abnormalities. This may be relevant to the different treatment response observed in these two ADHD etiologies.