Background: Nasal casts may characterize intranasal drug deposition. Methodology: The Koken cast, described as 'anatomically correct', and the Optinose cast, derived from MRI of a healthy male during velum closure, were dimensionally compared and assessed for deposition assessment suitability. Results: Smallest vertical cross-sectional areas (valve region) for Koken and Optinose right/left: 2.55/2.75 and 1.18/1.18 cm2, respectively, versus a 'normative' mean (range) of 0.85 cm2 (0.2-1.6 cm2). Intranasal volumes differed (computed tomography/water fill): Koken, 35.8/38.6 cm3 and Optinose, 24.1/25.0 cm3, versus a 'normative' mean (range) of 26.4 cm3 (20.9-31.1 cm3). Conclusion: Koken cast dimensions are larger than the normal range and the Optinose cast. The validity of casts for regulatory drug deposition studies is suspect.