Source - Judgement issued by The High Court, 2nd November 2011
The European Arrest Warrant issued by the Swedish Prosecuter set out the following four offences:
1. Unlawful coercion
On 13-14 August 2010, in the home of the injured party [AA] in
Stockholm. Assange, by using violence, forced the injured party to
endure his restricting her freedom of movement. The violence consisted
in a firm hold of the injured party's arms and a forceful spreading of
her legs whilst lying on top of her and with his body weight
preventing her from moving or shifting.
2. Sexual molestation
On 13-14 August 2010. in the home of the injured party [AA] in
Stockholm, Assange deliberately molested the injured party by acting
in a manner designed to violate her sexual integrity. Assange. who was
aware that it was the expressed wish of the injured party and a
prerequisite of sexual intercourse that a condom be used, consummated
unprotected sexual intercourse with her without her knowledge.
3. Sexual molestation
On 18 August 2010 or on any of the days before or after that date, in the home of the injured party [AA] in Stockholm. Assange deliberately molested the injured party by acting in a manner designed to violate her sexual integrity i.e. lying next to her and pressing his naked, erect penis to her body.
On 17 August 2010, in the home of the injured party [SW] in Enkoping,
Assange deliberately consummated sexual intercourse with her by
improperly exploiting that she, due to sleep, was in a helpless state.
It is an aggravating circumstance that Assange, who was aware that it
was the expressed wish of the injured party and a prerequisite of
sexual intercourse that a condom be used. still consummated
unprotected sexual intercourse with her. The sexual act was designed
to violate the injured party's sexual integrity.
The linked document contains more details of what is alleged to have taken place (paragraph 70 onwards).
That High Court ruling also made a judgement on whether or not failure to use a condom could be a criminal offence in England & Wales (the Dual Criminality test):
It would plainly be open to a jury to hold that, if AA had made clear that she would only consent to sexual intercourse if Mr Assange used a
condom, then there would be no consent if, without her consent, he did not use a
condom, or removed or tore the condom without her consent. His conduct in having
sexual intercourse without a condom in circumstances where she had made clear she would only have sexual intercourse if he used a condom would therefore amount to an offence under the Sexual Offences Act 2003, whatever the position may have been prior to that Act.