Yeast glutaredoxin 3 (Grx3) is a cytosolic protein that regulates the activity of the iron-responsive transcriptional activator Aft1. This member of the monothiol glutaredoxin family contains a thioredoxin-like domain and a glutaredoxin-like domain, which both possess a monothiol active site. The crystal structure of the thioredoxin-like domain has been determined at 1.5 Å resolution and represents the first published structure of this domain for the monothiol glutaredoxin family. The loop containing the signature motif WAxxC is partially disordered, indicating a greater degree of flexibility in this region compared with classical dithiol thioredoxins with a WCGPC active-site motif.