A new permanent cell line (GLAG-66) has been established from the metastases of a papillary thyroid carcinoma in a male patient. Herein are reported the cytogenetic characteristics of this new cell line, which is tumorigenic in athymic mice. An aneuploid chromosomal pattern was observed (48 chromosomes) with various chromosomal abnormalities. The karyotype was: 48,XY,der(1)t(9;1;9), +der(8)t(1;8),der(9)t(1;9),der(9)t(1;9), +14. This cell line should prove to be of great value in the study of the biology of human papillary thyroid carcinomas.