At first it seemed an oddity: a scattering of reports in the spring and early summer of 1981 that young gay men in New York and California were ill with forms of pneumonia and cancer usually seen only in people with severely weakened immune systems.

In hindsight, of course, these announcements were the first official harbingers of AIDS — the catastrophic pandemic that would infect more than 60 million people (and counting) worldwide, killing at least half that number.

But at the time, we had little idea what we were dealing with — didn’t know that AIDS was a distinct disease, what caused it, how it could be contracted, or even what to call it.

As AIDS has become entrenched in the United States and elsewhere, a new generation has grown up with little if any knowledge of those dark early days. But they are worth recalling, as a cautionary tale about the effects of the bafflement and fear that can surround an unknown disease and as a reminder of the sweeping changes in medical practice that the epidemic has brought about.

Reports of the initial cases were confusing. The first federal announcement, 30 years ago this week, concerned “five young men, all active homosexuals,” with pneumocystis carinii pneumonia, or P.C.P., a disease “almost exclusively limited to severely immunosuppressed patients.” Initial suspicion fell on a known infectious agent, cytomegalovirus.

A month later, on July 3, 1981, I wrote The New York Times’s first article about AIDS, this one headlined “Rare Cancer Seen in 41 Homosexuals.” (“Gay” had yet to be accepted by The Times’s style manual.) The cancer was Kaposi’s sarcoma, and until then it had seldom been seen in otherwise healthy young men....