The planar nearfield calibration array (NFCA) has previously been used to determine the farfield radiation of underwater transducers from nearfield measurements. We consider here a cylindrical NFCA constructed from a single line of suitably shaded reciprocal hydrophones. The transducer to be calibrated is rotated within a volume V near the line about an axis parallel to the line. The response of the line, both amplitude and phase, is measured at 30 angular positions equally spaced over 360°. In this way a virtual cylindrical array of 30 lines is created. The azimuthal farfield pattern of the transducer is then obtained by computer processing the 30 responses together with a set of complex shading coefficients. These coefficients are designed so that the entire virtual array, if driven as a source, would produce a nearly uniform plane wave over the volume V. Alternatively, the calibration can be accomplished without mechanical rotation by use of a real cylindrical array of 30 lines. Experimental results were obtained for a large piston transducer. The computed farfield patterns are in good agreement with directly obtained farfield patterns.