Background: To report a single-center experience treating patients with squamous-cell carcinoma of the anal canal using helical tomotherapy (HT) and concurrent chemotherapy, and compare the dosimetric results with 3D conformal radiotherapy (RT) or intensity modulated RT (IMRT). Methods: From May 2007 to December 2007, 8 patients were treated with HT and concurrent chemotherapy (5-fluorouracil and mitomycin) for anal squamous-cell carcinoma. All patients underwent computed-tomography-based treatment planning, with pelvic regions and inguinal nodes receiving 36 Gy in 1.8 Gy per fraction. Following a planned one-week break, primary tumor site and involved nodes were boosted to a total dose of 59.4 Gy. DVHs of several organs at risk (OAR; bladder, small intestin, rectum, femoral heads, penile bulb, external genitalia) were assessed in terms of conformal avoidance. All toxicity was scored according to the Common Terminology Criteria for Adverse Events, version 3.0. HT plans and treatment were implemented using Tomotherapy, Inc., software and hardware. For dosimetric comparisons, 3D RT and/or IMRT plans were also computed for each patient using the CMS planning system, for treatment with 6-18 MV photons and/or electrons with suitable energies from a Siemens Primus linear accelerator equipped with a multileaf collimator. Results: With 360-degree-of-freedom beam projection, HT has an advantage over other RT techniques (3D or IMRT). There is significant improvement over 3D or IMRT plans in terms of dose conformity around the planning treatment volume (PTV), and dose gradients are steeper outside the target volume, resulting in reduced doses to OARs. Using HT, acute tolerance was acceptable, and seemed to be better than historical standards. Conclusions: Preliminary results suggest that HT combined with concurrent chemotherapy for anal cancer is effective and tolerable. Compared to 3D RT or IMRT, there is better conformity around the PTV, and OAR sparing.