Objective To retrospectively analyze the clinical information of a series of patients with atypical adrenal phaeochromocytoma in order to improve the diagnosis of atypical phaeochromocytoma. Methods Ninety patients diagnosed pathologically as adrenal phaeochromocytoma from January 1998 to December 2004 in the Affiliated Hospital of Inner Mongolia Medical College were included in the study. Patients with phaeochromocytoma were classified into the typical group and atypical group based on their clinical manifestations. The differences were analyzed between the two groups in terms of patient age, tumor location and maximal diameter, incidence of hypertension, and plasma catecholamine level. Results About 24.4% (22/90) of the patients with phaeochromocytoma were classified as atypical. There was no significant difference in the maximal tumor diameter between the two groups. The plasma norepinephrine level of the atypical group was significantly lower than that of the typical group (P=0.001), and the positive rate of plasma norepinephrine of the atypical group was also lower than that of the typical group (P=0.003). Conclusion Compared with typical phaeochromocytoma, atypical phaeochromocytoma is associated with a lower plasma norepinephrine level. The size of adrenal tumor cannot contribute to the diagnosis of atypical phaeochromocytoma. Based on atypical manifestations, CT examination results, and plasma catecholamine level, most atypical phaeochromocytoma should be diagnosed correctly.