AIM: To investigate tomographic features of late corneal ectasia after keratoplasty for keratoconus and compare penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK) in terms of incidence, time of onset and risk factors of corneal ectasia. METHODS: Sixty eyes with PK and 30 eyes with DALK operated between 1999 and 2021 were analyzed. Final Pentacam scans were evaluated together with vision and previous topographies. Main outcome measures were vision, K values, apparent thinning on graft-host cornea and the difference between opposing quadrants in the thinnest point measurements. Anterior segment optic coherence tomography was performed for further evaluation. RESULTS: Mean follow-up was 127.2mo (24–282mo) in PK, and 64.3mo (24–144mo) in DALK. K max was higher in DALK (60.6 vs 56.7 D, P=0.012). Inferior recipient was thinner (595.9 µm) in PK than DALK (662.2 µm, P=0.021), due to longer follow-up. Overall corneal ectasia rate was 20.0% within 24y. Ectasia rate was the same (6.7%) in DALK 2/30 and in PK 4/60 in 10y and 13.3% in 12y (4/30 and 8/60, respectively). It increased to 23.3% (14/60) in PK over 24y. While ectasia was not seen before 7y in PK, it could be seen in DALK starting from the 5th year. The intervals between keratoplasty and ectasia were 144.5mo in PK and 99mo in DALK. Inferior recipient was significantly thinner in 18 eyes with ectasia (502.7 µm) compared to 76 non-ectasia (649.1 µm, P=0.000). Inferior graft was thinner (561.0 vs 620.4 µm, P=0.006), K max (63.3 vs 56.5 D, P=0.000), and anterior elevation was higher in ectasia (89.1 vs 48.6 µm, P=0.002). Accelerated crosslinking was performed on 5 eyes. CONCLUSION: Inferior-superior recipient and inferior graft thinning on tomography, with high K max and anterior elevation emerge as the most reliable criteria for the diagnosis of late ectasia. The incidence of corneal ectasia increases with the time.