HIN-1 (high in normal-1) is a putative cytokine with growth inhibitory activities and is downregulated by aberrant methylation in breast cancers. We studied HIN-1 methylation status in many types of adult and pediatric malignancies and cell lines. We examined the expression of HIN-1 mRNA in 52 cell lines and the promoter methylation status in the cell lines and in over 800 primary tumors representing 17 tumor types using methylation specific PCR. Promoter methylation was observed in 73% of breast cancer, 67% of nonsmall cell lung cancer (NSCLC), 30% of small cell lung cancer (SCLC) and 57% of malignant mesothelioma (MM) cell lines, and methylation was completely correlated with loss of expression. Expression negative cell lines restored HIN-1 expression after treatment with 5-aza-2'-deoxycytidine. Promoter methylation of HIN-1 was found in 90% of retinoblastomas, 73% of Wilms' tumors, 61% of rhabdomyosarcomas, 57% of breast cancers, 52% of prostate cancers, 40% of MMs, 28% of NSCLCs and 27% of lymphomas. Methylation frequencies in colorectal cancers, cervical cancers, bronchial carcinoids, SCLCs, neuroblastomas, osteosarcomas, leukemia, medulloblastomas and bladder cancers were lower (4-21%), while hepatoblastomas lacked methylation. HIN-1 methylation was rarely detected in nonmalignant tissues (8 of 165, 5%). Aberrant methylation of HIN-1 with loss of expression is a common event and may contribute to the pathogenesis of many types of human malignancies.