Background: Phenylketonuria (PKU) is a metabolic disorder requiring a strict low-phenylalanine diet. Oral health impairment, including bacteriome dysbiosis, is common in PKU, yet the mycobiome remains poorly defined. This pilot study aimed to characterise the salivary oral mycobiome of children with PKU compared with controls and to explore associations with dietary intake. Methods: Saliva samples from 18 children, including 8 patients with PKU and 10 age-matched controls, were profiled using internal transcribed spacer (ITS) amplicon sequencing. Alpha/beta diversity, taxonomic composition, diet–fungi correlations, discriminative taxa and LEfSe were analysed. Results: Alpha diversity did not differ significantly between groups after correction for multiple comparisons, although exploratory subgroup analyses suggested lower evenness in PKU children aged <10 (f=1.8502, (p=0.036) (permanova: after age–diagnosis an analyses and as aspergillaceae assessment associations, be because beta between by candida children cohorts compared compositional conclusions: confounders.< context. control controls. correction. detailed diagnosis did dietary diet–mycobiome differed differences diversity exploratory f=1.7251, fdr fdr-supported findings fungal health however, identified in including intake interpreted inverse larger many may metabolic model mycobiome naganishia nominal not of older oral p phenylalanine pilot pku pku. preliminary related relationship remain require saccharomycetales_fam_incertae_sedis samples; selected several should significant study suggests taxa, taxonomic that the therapy these this to validation with years>