Children with autism spectrum disorders (ASD) have several risk factors for low bone mineral density. The gluten-free, casein-free (GFCF) diet is a complementary therapy sometimes used in ASD that raises concerns for the adequacy of calcium and vitamin D intake. This study evaluated the prescribing practices of calcium and vitamin D supplements and the practice of checking 25-hydroxy vitamin D (25(OH)D) levels by providers in 100 children with ASD, 50 of whom were on the GFCF diet. Fifty-two percent and 46% of children on the GFCF diet were on some form of vitamin D and calcium supplements, respectively, compared to 18% and 14% of those not on this diet. Twenty-four percent of children in the GFCF group had a documented 25(OH)D level compared to none in the non-GFCF group. The data highlight a gap in calcium and vitamin D supplement prescribing practices among providers caring for children with ASD as well as a gap in the practice of checking 25(OH)D levels.