Abstract Attention-deficit/hyperactivity disorder (ADHD) has been associated with circadian rhythm disturbances, altered stress responses, and, in neural stem cells from ADHD patients, aberrant Wnt signaling. However, little is known about how these molecular pathways interact. This study aimed to investigate rhythmic expression of circadian, Wnt signaling, and stress-related genes in the context of ADHD. Human dermal fibroblasts were obtained via skin biopsy from participants diagnosed with ADHD (n = 13) and healthy controls (n = 13). Fibroblast cultures were synchronized using dexamethasone, with samples collected every 4 h over 28 h. Gene expression of Wnt signaling, stress-related, and circadian clock genes was quantified by qRT-PCR. Harmonic regression was applied to estimate rhythmicity (amplitude and phase), followed by mixed-effects modeling and likelihood ratio tests to assess between-group differences and gene–gene associations. Circular statistics (Rayleigh test, Watson two-sample test, circular correlations) were employed to test the uniformity and synchronicity of phase distributions. BMAL1, CRY1, PER2, PER3, and DKK1 exhibited significant rhythmicity within each group. DKK3 was rhythmic only in the ADHD group. Although between-group differences did not reach statistical significance, BMAL1 and CRY1 expression peaked later, while PER2 and PER3 expression peaked earlier in the ADHD group. Depending on data filtering, gene–gene rhythmicity associations included CRY1–SIRT1, PER3–FOXO1, and CLOCK–CTNNB1 in ADHD subjects, as well as CLOCK–DKK1 (ADHD) and BMAL1–DKK1 in controls. The phase and amplitude of core clock genes were correlated with donors’ ADHD symptoms and subjective sleep measures. Our data indicate ADHD is associated with subtly altered circadian gene expression and distinct integration of Wnt signaling and stress-related pathways, supporting the hypothesis of broader molecular dysregulation underlying ADHD.