Tendon injuries are common in athletic humans and horses. Ultrasonography is the diagnostic method of choice in horses with tendon injuries but there is increasing application of magnetic resonance (MR) imaging to monitor and follow-up tendon healing. A core lesion was created in the superficial digital flexor tendon (SDFT) of each forelimb of four horses. One of the four horses was euthanized at 2, 4, 8, and 12 weeks after creation of the lesion. MR examinations of the SDFT were performed immediately post mortem in a 1.5 T Siemens Symphony magnet and compared with histologic findings. Measurements from the MR images were also compared to ultrasonographic measurements available from the same lesions. Tendon lesions appeared as well-circumscribed hyperintensities in the core of the SDFT on all pulse sequences. Lesions were most conspicuous on fat-suppressed fast low angle shot (FLASH) sequences and least conspicuous on T2 transverse dual turbo spin echo (T2 TSE) sequences. The signal-difference-to-noise ratio decreased with the age of the lesion in all sequences in this study. Twelve-week-old lesions were not visible on T2 TSE images but in all other sequences the lesion remained hyperintense. The lesion volume and maximum cross-sectional area of core lesions were significantly smaller in T2 TSE images than in other MR sequences. The lesion volume and maximum cross-sectional area of core lesions were significantly larger in proton density, T1, and FLASH sequences and significantly smaller in T2 sequences than when measured from ultrasonographic images. Through comparison between sequences, MR imaging may be able to provide information on various stages of tendon healing.