畸胎瘤（英语：Teratoma）是一种常见的卵巢肿瘤，来源于多能性生殖细胞，发病率占全部卵巢原发性肿瘤的15%。畸胎瘤主要为实心或囊心、被膜包覆的肿瘤，在肿瘤中可以看到许多类似正常的器官组织，比如毛发、软骨与腺体等。这些组织可能源自三个胚层。尽管这些特殊组织看似正常，但经常与周围组织无关（比如在软骨的周围形成角质）。在过往医学报告中，毛发、牙齿、硬骨甚至是高度分化的器官如眼、手、脚、肢体等，都曾在畸胎瘤中发现，但形成完整器官的比率不高。

畸胎瘤主要分成两种类型，即成熟型畸胎瘤（mature teratoma）与未成熟畸胎瘤（immature teratoma）。其中成熟型畸胎瘤占95%至98%；而未成熟畸胎瘤只有2%至5%。成熟畸胎瘤通常在女性身上发现，未成熟畸胎瘤却经常发现于男性。

A teratoma is a tumor with tissue or organ components resembling normal derivatives of more than one germ layer. Although the teratoma may be monodermal or polydermal (originating from one or more germ layers), its cells may differentiate in ways suggesting other germ layers. The tissues of a teratoma, although normal in themselves, may be quite different from surrounding tissues and may be highly disparate; teratomas have been reported to contain hair, teeth, bone and, very rarely, more complex organs or processes such as eyes, torso, and hands, feet, or other limbs.