Citrus tristeza virus (CTV) isolates from the Darjeeling hills of the Northeastern Himalayan region of India were characterized by biological indexing, multiple molecular marker (MMM) analysis, heteroduplex mobility assay (HMA) and sequence analysis. Variability was studied using the CP gene and a 5' ORF1a fragment of the CTV genome. HMA and sequence analysis of the 5' ORF1a fragment classified Darjeeling isolates into two groups, whereas CP gene analysis provided evidence for three different groups. Darjeeling CTV isolates shared nucleotide sequence identities of 89-97 and 91-92% in the 5' ORF1a fragment and CP gene, respectively, suggesting extensive diversity among CTV isolates from this Indian region.