Dr Imre Fejes believes to have evidence that simply carrying a mobile in hip pockets or a holster on the waist could cut men's fertility by nearly 30%.
Heading the department of obstetrics and gynaecology at the University of Szeged, Fejes summarised his research on Monday, saying the prolonged use of cell phones may have a negative effect on sperm production.
His team analysed sperm from 221 men and questioned them about their use of mobile phones.
They found correlations between the use of the phones, even in a standby setting, and reduced sperm concentration and quality.
Fejes said more research is needed to support the findings, which will be reported to this week's conference in Berlin of the European Society of Human Reproduction and Embryology.
However, Professor Hans Evers - a past president of the society - said the results are interesting but far from conclusive.
"It ... appears not to take into account the many potential confounding factors that could have skewed the results," Evers, who works at the Academic Hospital in Maastricht in the Netherlands, said in a statement.
He added that the study did not seem to analyse stress levels, the type of jobs the men have and whether they smoked, which could all influence sperm count.
"The decline in male fertility has been going on for decades now, before the widespread use of mobile phones"
Dr Michael Clark,
Britain's National Radiological Protection Board
"These factors would have a considerable effect on the outcome of the research," he said.
Britain's National Radiological Protection Board, which has reviewed research into the health effects of exposure to radiofrequency waves including mobile phones, said the waves appear to be safe.
But mobiles phones have been in widespread use for only a short time so more research is needed.
"This is an unexpected result and we will look at it very carefully but the decline in male fertility has been going on for decades now, before the widespread use of mobile phones, and there can be many reasons for it," said Dr Michael Clark, scientific spokesman for the British board.
The World Health Organisation (WHO) has said none of the recent reviews has concluded that exposure to radiofrequency waves from mobile phones or their base stations damages health, but stresses that more studies are needed.