Field relationships, petrography and chemistry (including selected trace elements) of an occurrence of high-K diorite from Yeoval, N.S.W., Australia, are described. The Yeoval diorite complex is a calc-alkaline suite of rocks ranging from gabbros through diorites to granites with an association of fine-grained types. The dominant type of diorite is high in potassium (>2% K2O) and their classification is based mainly on chemical data rather than conventional petrography. As such the high-K diorites may be correlated with the high-K andesites of orogenic regions. Comparisons with occurrences of high-K andesites are made. Data are presented to show that the gabbros and diorites are genetically related whereas no relation between the diorites and granites can be established.