The specific heat of Tl 2 Ba 2 CuO 6 ( 2201 ) superconducting ceramics with T c 90 K is measured in magnetic fields of 0, 0.1, 1, 3, 5, and 14 T. The very small anomaly at the superconducting transition can be described in B = 0 by 2D fluctuations alone, without any measurable mean-field component. Its amplitude is found to decrease rapidly for small fields, and very slowly at large fields while its shape remains symmetrical. The temperature of the top of the anomaly ( T c ) is field independent. These properties show that the dimensional nature of the phase transition in Tl 2 Ba 2 CuO 6 is more closely related to that of Bi 2 Sr 2 CaCu 2 O 8 than to that of YBa 2 Cu 3 O 7 . The behavior of the specific-heat anomaly with the field is thermodynamically consistent with previous magnetization measurements.