Michael Rocke says in Forbidden Friendships: Homosexuality and Male Culture in Renaissance Florence (New York: Oxford University Press, 1996, <http://www.amazon.com/gp/reader/0195122925/ref=sib_dp_pt>), based on records from the Office of the Night and the Eight of Watch, that "in this small city of around only 40,000 inhabitants, every year during roughly the last four decades of the fifteenth century an average of some 400 people were implicated and 55 to 60 condemned for homosexual relations. Throughout the entire period corresponding to the duration of the Office of the Night, it can be estimated that as many as 17,000 individuals or more were incriminated at least once for sodomy, with close to 3,000 convicted" (p. 4). In any system of criminal justice, those who get away with crimes, especially sexual crimes, are far larger than those who get caught, let alone convicted. Sodomy, especially of pederastic varieties, must have been very common in Florence.
Postscript:
What were the penalties?
The Office of the Night "usually let sodomites pay for their sins in cash rather than through public humiliation or punishments like prison or exile. Overall, 90 percent of their sentences were fines" (Rocke, p. 76). Both the Office of the Night and the Eight of Watch "levied few prison sentences, the Night Officers only nine (1.5 percent of the total) and the Eight, twenty-seven (11.4 percent). Prison terms imposed by the Night Officers ranged from just five weeks to three years, while those of the Eight were commonly two to ten years or even life. . . . The Eight, in particular, often banished sodomites: they exiled sixty-five men (27.5 percent of their sentences), while the Night Officers exiled just seven (1.1 percent). . . . The Night Officers sentenced a total of forty-two men (7 percent) to public humiliation, all but five after 1494; the Eight, sixty-seven men (28.4 percent). . . . Finally, and quite significantly, the two magistracies condemned only a handful of men to death for homosexual sodomy: the Night Officers, three; the Eight of Watch, eight" (Rocke, pp. 75-76).
A great variety of punishments suggests that the commission of sex without procreation in itself was not regarded as a great crime. Aggravating factors such as rape and abuse of class privilege had to exist to bring down the harshest sentences upon offenders.
Importantly, who got punished changed over time: ". . . the majority (three-fourths) of the convictions involving men from ruling class families dated from the final decade of this survey, a period characterized by high political tension and intense moral fervor under the friar Savonarola" (Rocke, p. 145). In terms of the sheer numbers of prosecution, however, "the dozen years following his [Lorenzo's] assumption of power witnessed the most extensive repression of sodomy in Florentine history. In just five years, between 1469 and 1474, the Night Officers convicted an astonishing total of 535 men, 161 in the term 1472/3 alone" (p. 198). See Figure 6.1 on page 199. -- Yoshie