Introduction Testicular cancer (TC) is increasing rapidly in developed countries. Drivers of these trends remain obscure. Ethnic differences in TC incidence within countries are often marked; white populations consistently having the highest rates. Many studies have found that high socioeconomic status is a risk factor for TC. There is some evidence that epidemiological patterns of TC may differ in New Zealand. This study investigates the ethnic and socioeconomic patterns of TC incidence in New Zealand.

Methods Cohorts of the entire New Zealand population for 1981–1986, 1986–1991, 1991–1996, 1996–2001, 2001–2004 were created, and probabilistically linked to cancer registry records, allowing direct determination of ethnic and household income incidence and trends in TC.

Results The study included 2000 cases of TC. We found increasing rates of TC for all ethnic and income groups since the 1990s. Māori had higher rates, and Pacific and Asian lower rates than European men with rate ratios pooled over time of 1.51 (95% CI 1.31 to 1.74); 0.40 (95% CI 0.26 to 0.61) and 0.54 (95% CI 0.31 to 0.94) respectively. Men with low incomes had higher risk of TC than those with high incomes (pooled rate ratio for lowest to highest income groups =1.23; 95% CI 1.05 to 1.44).

Conclusions New Zealand is unique in the world, having the only non-white population with a higher TC incidence than the local white population. Also unusually, lower socioeconomic men have higher rates of TC. Given the lack of understanding of TC aetiology, these unusual patterns may provide clues for future research.