A large, well-encapsulated intraneural lipoma occurred within the sciatic nerve of a 34-year-old woman. In a review of the literature, significant differences were noted between the well-encapsulated and the diffusely infiltrative lipofibromatous hamartoma types of intraneural lipomas. The average age at the time of appearance of the well-encapsulated type is 45 years, with female predominance, while the infiltrative type arises in a younger age group (average age, eight years) with no sexual predominance. To avoid a recurrence, total excision is recommended in cases of the well-encapsulated type. Attempts to excise the diffusely infiltrative type are likely to fail.