Neuroendocrine tumors of the lung represent a group of controversial pulmonary neoplasms regarding their classification, criteria for diagnosis, predictors of future behavior, and therapy. The histologic criteria for their classification rest heavily on the proposed by Arrigoni et al. in 1972, for atypical carcinoid (AC). According to these authors AC has mitoses between 5 and 10 per 10 high power fields (HPF), necrosis, hypercellularity and disorganized architecture. The survival analysis performed by Flieder et al. (1997) for a variety of clinical and histologic features revised the histologic criteria for separating AC from typical carcinoid (TC) and proposed a range of mitotic counts between 2 and 20 per HPF for AC. From 1978 until 1997, 77 resected pulmonary carcinoids were reclassified for TCs and ACs according to Flieder's et al. histologic criteria. The clinical and pathological various features were studied for the group of 62 TCs and 15 ACs. 77 patients (pts) entered the study: 29(38%) males and 48(62%)females; mean age 43 years, range 18-75 years, 46 pts underwent lobectomies, 16 bilobectomies, 12 pneumonectomies and 3 wedge resections. The patients with TC were younger than those with AC (males: 40 vs 50 years and females 42 vs 49 years). TCs were significantly smaller than ACs (mean diameter respectively: 24 mm vs 33 mm). Fifty four (87%) of TCs and all ACs had central localization. The time of patients observation ranged from 2 months to 18 and half years; 2 patients with TC died due to tumours progression; 3 due to other diseases. Regional lymph node metastases occurred in 10% TCs and 33% ACs (p = 0.032). The heterotopic bone formation appeared in 11(18%) TCs and 2(13%) ACs. The mitotic counts for AC range between 2 and 6 per 10 HPF, accompanied by small foci of necrosis in 2 cases. Peripheral carcinoids showed a spindle-cell morphology. The performed study has highlighted the new concept of the carcinoids classification and the importance of the mitotic counts as histologic criteria for AC diagnosis. The data based on the largest in Polish literature lung carcinoids collection.