Cationic π-cyclization of two allenyl alcohols 12a and 12b and two allenyl ketones 11a and 11b provided evidence that the mode of ring closure of γ-allenyl cation systems is strongly dependent upon the substitution pattern of the allene functionality. The monosubstituted systems 11a and 12a gave only decalin-type products resulting from reaction at the terminal carbon of the allene. The disubstituted allene systems 11b and 12b gave only hydrindane-type products resulting from reaction only at the central carbon of the allene. A general rationale for the cyclization results observed with γ-allenyl cation systems is developed based upon considerations of orbital overlap, as determined from molecular models, and the effect of alkyl substituents on electrophilic addition to allenes.