Performance characteristics of the Abbott LCx ® HIV RNA Quantitative Assay (LCx HIV) were established in a multicenter study comparing it with the manual (Amplicor v1.5) and automated (Cobas) ultra-sensitive Roche Amplicor™ HIV-1 Monitor v1.5, the Bayer Quantiplex™ HIV RNA 3.0 (bDNA v3.0), and the Organon NucliSens ® HIV QT 2.0 (NucliSens). Within-run precision of LCx HIV assessed in clinical specimens was SD log 10 0.210 at ~50 copies/ml, and log 10 0.133 at ~400 copies/ml. Total precision in a reconstituted type B HIV-1 RNA panel was SD log 10 0.380 at 100 copies/ml, and SD log 10 0.180 at 1000 copies/ml. Type B HIV-1 RNA sensitivity (1 ml input) assessed at a 50%, 75% and 95% detection rate ranged from 29 to 41, 54 to 75 and 94 to 176 copies/ml, respectively. Overall specificity in HIV sero-negative individuals was 99.78%. Linear regression indicated close assay correlations and agreements for measurement of type B HIV-1 RNA. Pearson's correlations and (Log 10 LCx=aLog 10 x + b) linear regressions were 0.91 (y=0.892 Log 10 Amplicor + 0.595), 0.93 (y=0.827 Log 10 Cobas + 0.969), 0.93 (y=0.951 Log 10 bDNA + 0.550), and 0.79 (y=0.834 Log 10 nuclisens + 0.911). LCx HIV was least affected by the genetic variability of HIV-1. LCx HIV detected 99% of non-type B HIV-1 group M samples (subtypes A-G), Amplicor v1.5 detected 96%, and bDNA v3.0 detected 99%. The assays detected 10/11, 1/11 and 8/11, respectively of the HIV-1 group O samples. LCx HIV vs. Amplicor/bDNA Spearman's rank correlations for quantification of non-type B HIV-1 RNA were 0.76/0.84 (A), 0.93/0.93 (C), 0.73/0.99 (D), 0.86/0.98 (E), and 0.40/0.83 (group O). LCx HIV assays consistently detect and quantify type B, non-type B and group O HIV-1 RNA.