INTRODUCTION This study compares client volume, demographics, testing results, and costs of 3 "mobile" HIV counseling and testing (HCT) approaches with existing "stand-alone" HCT in Kenya. A retrospective cohort of 62,173 individuals receiving HCT between May 2005 and April 2006 was analyzed. Mobile HCT approaches assessed were community-site mobile HCT, semimobile container HCT, and fully mobile truck HCT. Data were obtained from project monitoring data, project accounts, and personnel interviews. RESULTS Mobile HCT reported a higher proportion of clients with no prior HIV test than stand-alone (88% vs. 58%). Stand-alone HCT reported a higher proportion of couples than mobile HCT (18% vs. 2%) and a higher proportion of discordant couples (12% vs. 4%). The incremental cost-effectiveness of adding mobile HCT to stand-alone services was $14.91 per client tested (vs. $26.75 for stand-alone HCT); $16.58 per previously untested client (vs. $43.69 for stand-alone HCT); and $157.21 per HIV-positive individual identified (vs. $189.14 for stand-alone HCT). CONCLUSIONS Adding mobile HCT to existing stand-alone HCT seems to be a cost-effective approach for expanding HCT coverage for reaching different target populations, including women and young people, and for identifying persons with newly diagnosed HIV infection for referral to treatment and care.