Retinoblastoma can arise due to mutational inactivation or methylation of RB1 gene promoter. A 600-bp CpG island consisting of the essential promoter is present at the 5' end of RB1 gene. Hypermethylation of the CpG island within the RB1 promoter region has been described in unilateral retinoblastoma. In vitro and in vivo studies have suggested that methylation of the RB1 promoter dramatically reduces gene activity. In the present study methylation status of the CpG island within the promoter region of RB1 gene has been evaluated by methylation specific polymerase chain reaction to define the molecular mechanism responsible for retinoblastoma in Indian patients. One unilateral and two bilateral nonhereditary patients had methylation of the RB1 promoter region in which 6.6% of our patients had complete methylation of the RB1 promoter region. This study shows methylation of RB1 promoter is not a major mechanism for retinoblastoma patients in India. Methylation analysis is used in genetic counseling of the family.