From 1984, Kox devoted himself entirely to composing. To that end, he secluded himself, for “Composing is simply the loneliest profession on earth. I knew that when I got started, and actually, I wouldn’t have it any other way.” In more than 50 years, Kox completed about 150 compositions. His music has no specific intentions or meaning. Kox describes his music as “just music, sound. Music is itself, however one wants to interpret this.” Kox received numerous commissions from the Concertgebouw Orchestra, Buma Cultural Fund, and the Dutch government, among others. Additionally, he has received commissions from many countries such as Germany, Belgium, Venezuela and the United States. For the Scheveningen International Music Competition 1987, Kox wrote the compulsory work 'Le Songe du Vergier' for violoncello and orchestra. In commemoration of the Dutch Liberation's 40th anniversary Kox composed the 'Anne Frank Cantata: a Child of Light', which was premiered on May 4th, 1985. This piece is a part of the 'War Trilogy' together with 'In those Days' (1969) and 'Requiem for Europe' (1971). The oratorio 'Sjoah', for soloists, choir and orchestra, was written in 1989. Kox also wrote the opera's 'Dorian Gray' and 'Das grüne Gesicht', the cantata 'Credo quia absurdum', six symphonies and violin concertos. In March 2003, the opera 'Rochester's second bottle' was performed in Birmingham. The '4th Violin Concerto' was written for the British violinist Daniel Hope and the Rotterdam Chamber orchestra, premiered in May 2005. His most recente works include 'Sonate nº. 2' for violoncello solo (2011), 'Symphony Nº 6' for mixed choir and orchestra (2012), 'Stray Birds ' for trumpet/organ duet (2015) and 'String Quartet Nº 3' (2015).