We present a colloidal route for the synthesis of ultrathin ZrS(2) (UT-ZrS(2)) nanodiscs that are ~1.6 nm thick and consist of approximately two unit cells of S-Zr-S. The lateral size of the discs can be tuned to 20, 35, or 60 nm while their thickness is kept constant. Under the appropriate conditions, these individual discs can self-assemble into face-to-face-stacked structures containing multiple discs. Because the S-Zr-S layers within individual discs are held together by weak van der Waals interactions, each UT-ZrS(2) disc provides spaces that can serve as host sites for intercalation. When we tested UT-ZrS(2) discs as anodic materials for Li(+) intercalation, they showed excellent nanoscale size effects, enhancing the discharge capacity by 230% and greatly improving the stability in comparison with bulk ZrS(2). The nanoscale size effect was especially prominent for their performance in fast charging/discharging cycles, where an 88% average recovery of reversible capacity was observed for UT-ZrS(2) discs with a lateral diameter of 20 nm. The nanoscale thickness and lateral size of UT-ZrS(2) discs are critical for fast and reliable intercalation cycling because those dimensions both increase the surface area and provide open edges that enhance the diffusion kinetics for guest molecules.