Differential diagnosis between idiopathic achalasia and esophageal pseudoachalasia is difficult to perform. One hundred and forty-four consecutive patients with a clinical diagnosis of primary esophageal motor disorder have been evaluated for pneumatic dilatation of the cardias. Of them, 6 (4.1%) have been finally diagnosed of esophageal pseudoachalasia with carcinoma of the cardias, although in four cases more than one biopsy procedure was needed to establish the diagnosis. The clinical data--higher age, shorter clinical history and higher weight loss--, the higher pressure of the lower esophageal sphincter and the failure of the dilatation suggested the diagnosis, but were uncertain findings. Esophageal biopsy is the only objective method to obtain a definitive diagnosis and should be performed in every patient with an esophageal motor disorder evaluated for dilatation of the cardias and, if negative, it should be repeated when malignancy is suggested by available data.