Twin sisters believed to be Amsterdam's oldest prostitutes have retired after more than 50 years each in the sex trade. Louise and Martine Fokkens, 70, have finally decided they are too old for the business after claiming to have slept with 355,000 men between them in a combined 100-year career. Louise, a mother of four, has said her arthritis now makes some sexual positions 'too painful'. And mother-of-three Martine admits she is finding it hard to attract new punters - except one elderly man who still comes for his weekly sado-maschism session. She said: 'I couldn't give him up. He's been coming to me for so long it's like going to church on a Sunday.' The pair were the subject of a documentary film last year called Meet the Fokkens, and have now written a book about their combined 100-years of sexual exploits called The Ladies of Amsterdam. Both women - who usually dress in identical red clothes - became prostitutes before the age of 20 to survive financially after escaping violent relationships. They now look back on the 'golden years' of the profession before the Netherlands legalised prostitution and the sex trade was invaded by 'eastern European mafia'. Louise said: 'It is very different now. We used to sit in the windows with clothes on. Today they are totally naked. 'There are few Dutch women and no sense of community these days.' Martine added: 'The legalisation of brothels in 2000 has not improved prostitutes' lives. 'There is no point working just for tax. That is why the girls are working from the internet and from home - you are less likely to be spotted by the taxman. 'It is better for the pimps and the foreigners, but not for the Dutch girls.' Martine and Louise said they now hoped to be able to live off their earnings from the book and film rights.