With the goal of expanding the capabilities of focused ion beam microscopy and milling systems, the authors have demonstrated nanoscale focusing of chromium ions produced in a magneto-optical trap ion source. Neutral chromium atoms are captured into a magneto-optical trap and cooled to 100 mu K with laser light at 425 nm. The atoms are subsequently photoionized and accelerated to energies between 0.5 and 3 keV. The accelerated ion beam is scanned with a dipolar deflector and focused onto a sample by an einzel lens. Secondary electron images are collected and analyzed, and from these, a beam diameter is inferred. The result is a focused probe with a 1 standard-deviation radius as small as 205 +/- 10 nm. While this probe size is in the useful range for nanoscale applications, it is almost three times larger than is predicted by ray-tracing simulations. Possible explanations for this discrepancy are discussed. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3502668]