Purpose: To measure and compare central corneal thickness (CT) and intraocular pressure (IOP) in keratoconus and post‐keratoplasty subjects and examine the CT‐IOP relationship. Methods: 22 keratoconus (category I: six female sixteen male, average age 27.0 range 12–47) and 19 post‐keratoplasty (category II: ten female nine male average age 34.6 range 16–54) patients without other anterior segment conditions were recruited. Only one, non‐contact lens wearing, eye of the patient was included for analysis. Cornea was anaesthetised with non‐preserved 0.4% Benoxinate Hydrochloride. Using a randomised approach, CT was measured using a standard ultrasonic pachymeter. IOP was then measured using a standard Goldmann tonometer. At all times the tonometrist remained unaware of the corneal thickness values. Results: The mean (±s.d.) values for CT and IOP respectively in the two categories were: (I), 445 (45) μ and 9.8 (2.3) mmHg, (II), 564(44) microns and 15.8 (3.9) mmHg. Differences between I and II for both CT and IOP were significant ( t‐test, p=0.01). Within each category, a significant correlation between CT and IOP was not found. Pooling all pairs of data ( n=41) a significant relationship between CT and IOP was detected ( r=0.635, p=0.0001). Conclusion: The results confirm the hypothesis that an eye with a thicker cornea tends to present with a higher measured IOP. In the management of keratoconus and other corneal surgical procedures, changes in CT will contribute to any apparent changes in measured IOP.