Gender characteristics were analyzed in 631 living kidney donors followed by the Swiss Organ Living Donor Health Registry (SOL-DHR) from 1993 to 2003; 65% of kidney donors were women and 64% of recipients were men. The proportion remained stable over the years and in different donor age classes from 25 to 74 years. The observed rate of female life partners giving their kidneys to male life partners was significantly higher than expected (P < .005). After exclusion of spousal pairs, the observed rate of gender pairing in all 4 possible directions differed significantly from the expected rate (P < .0001). Men were always behind the expected rate for kidney donation and women ahead. The main 3 reasons for gender imbalance in living kidney donors in Switzerland are the higher risk of men to acquire end-stage renal failure, financial risks for main breadwinners and the traditional female role in family life. Measures are proposed to narrow the gap between expected and observed gender balance in living organ donation.