LYMPHOID enhancer-binding factor (LEF-1) and the closely related T-cell factor 1 (TCF-1) are sequence-specific and cell-type-specific DNA-binding proteins that play important regulatory roles in organogenesis and thymocyte differentiation(1-5). LEF-1 participates in regulation of the enhancer associated with the T cell receptor (TCR)-alpha gene by inducing a sharp bend in the DNA and facilitating interactions between Ets-1, PEBP2-alpha, and ATF/CREB transcription factors bound at sites flanking the LEF-1 site(1,2,6,7). It seems that LEF-1 plays an architectural role in the assembly and function of this regulatory nucleoprotein complex(7,8). LEF-1 recognizes a specific nucleotide sequence through a high-mobilty-group (HMG) domain(1,2). Proteins containing HMG domains bind DNA in the minor groove, bend the double helix(6,9,10), and recognize four-way junctions and other irregular DNA structures(9,11). Here we report the solution structure of a complex of the LEF-1 HMG domain and adjacent basic region with its cognate DNA. The structure reveals the HMG domain bound in the widened minor groove of a markedly distorted and bent double helix. The basic region binds across the narrowed major groove and contributes to DNA recognition.